add missing Timestamp to Votes

Fixes:

```
panic: Panicked on a Sanity Check: can't encode times below 1970 [recovered]
        panic: Panicked on a Sanity Check: can't encode times below 1970

goroutine 2042 [running]:
testing.tRunner.func1(0xc420e8c0f0)
        /usr/local/go/src/testing/testing.go:711 +0x5d9
panic(0xcd9e20, 0xc420c8c270)
        /usr/local/go/src/runtime/panic.go:491 +0x2a2
github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common.PanicSanity(0xcd9e20, 0xf8ddd0)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common/errors.go:26 +0x120
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.WriteTime(0x0, 0x0, 0x0, 0x1306440, 0xc4201607e0, 0xc420e31658, 0xc420e31680)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/time.go:19 +0x11e
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.writeReflectBinary(0xdc9e40, 0xc4201fcf30, 0x199, 0x1317b80, 0xdc9e40, 0xc98451, 0x9, 0x0, 0xdc9e40, 0xc420ead9c0, ...)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/reflect.go:525 +0x22f0
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.writeReflectBinary(0xd25400, 0xc42000e2e8, 0x196, 0x1317b80, 0xd92d60, 0xc9a195, 0xa, 0x0, 0xcc8ce0, 0xc420164920, ...)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/reflect.go:530 +0x21e7
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.writeReflectBinary(0xcc8ce0, 0xc4209f95b8, 0x197, 0x1317b80, 0xcc8ce0, 0xc9a195, 0xa, 0x0, 0xcc8ce0, 0xc420164920, ...)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/reflect.go:518 +0x2509
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.writeReflectBinary(0xd873e0, 0xc4209f9580, 0x16, 0x1317b80, 0xd79400, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/reflect.go:530 +0x21e7
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.WriteBinary(0xd873e0, 0xc4209f9580, 0x1306440, 0xc4201607e0, 0xc420e31658, 0xc420e31680)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/wire.go:80 +0x15f
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire.BinaryBytes(0xd873e0, 0xc4209f9580, 0x3, 0x8, 0xc420160798)
        /go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-wire/util.go:15 +0xb8
github.com/tendermint/tendermint/blockchain.(*BlockStore).SaveBlock(0xc4201342a0, 0xc420eac180, 0xc420130640, 0xc4209f9580)
        github.com/tendermint/tendermint/blockchain/_test/_obj_test/store.go:192 +0x439
github.com/tendermint/tendermint/blockchain.TestBlockStoreSaveLoadBlock(0xc420e8c0f0)
        /go/src/github.com/tendermint/tendermint/blockchain/store_test.go:128 +0x609
testing.tRunner(0xc420e8c0f0, 0xf20830)
        /usr/local/go/src/testing/testing.go:746 +0x16d
created by testing.(*T).Run
        /usr/local/go/src/testing/testing.go:789 +0x569
exit status 2
FAIL
```

blockchain/store_test.go

@@ -12,7 +12,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"github.com/tendermint/go-wire"
+	wire "github.com/tendermint/go-wire"
 	"github.com/tendermint/tendermint/types"
 	"github.com/tendermint/tmlibs/db"
 	"github.com/tendermint/tmlibs/log"
@@ -104,7 +104,7 @@ var (
 	partSet     = block.MakePartSet(2)
 	part1       = partSet.GetPart(0)
 	part2       = partSet.GetPart(1)
-	seenCommit1 = &types.Commit{Precommits: []*types.Vote{{Height: 10}}}
+	seenCommit1 = &types.Commit{Precommits: []*types.Vote{{Height: 10, Timestamp: time.Now().UTC()}}}
 )
 
 // TODO: This test should be simplified ...
@@ -124,7 +124,7 @@ func TestBlockStoreSaveLoadBlock(t *testing.T) {
 	// save a block
 	block := makeBlock(bs.Height()+1, state)
 	validPartSet := block.MakePartSet(2)
-	seenCommit := &types.Commit{Precommits: []*types.Vote{{Height: 10}}}
+	seenCommit := &types.Commit{Precommits: []*types.Vote{{Height: 10, Timestamp: time.Now().UTC()}}}
 	bs.SaveBlock(block, partSet, seenCommit)
 	require.Equal(t, bs.Height(), block.Header.Height, "expecting the new height to be changed")
 
@@ -143,7 +143,7 @@ func TestBlockStoreSaveLoadBlock(t *testing.T) {
 
 	// End of setup, test data
 
-	commitAtH10 := &types.Commit{Precommits: []*types.Vote{{Height: 10}}}
+	commitAtH10 := &types.Commit{Precommits: []*types.Vote{{Height: 10, Timestamp: time.Now().UTC()}}}
 	tuples := []struct {
 		block      *types.Block
 		parts      *types.PartSet
@@ -369,7 +369,7 @@ func TestBlockFetchAtHeight(t *testing.T) {
 	block := makeBlock(bs.Height()+1, state)
 
 	partSet := block.MakePartSet(2)
-	seenCommit := &types.Commit{Precommits: []*types.Vote{{Height: 10}}}
+	seenCommit := &types.Commit{Precommits: []*types.Vote{{Height: 10, Timestamp: time.Now().UTC()}}}
 
 	bs.SaveBlock(block, partSet, seenCommit)
 	require.Equal(t, bs.Height(), block.Header.Height, "expecting the new height to be changed")