Make benchmarks a real package for go get ./...

benchmarks/chan_test.go

@@ -1,4 +1,4 @@
-package main
+package benchmarks
 
 import (
 	"testing"

benchmarks/empty.go

@@ -0,0 +1 @@
+package benchmarks

benchmarks/map_test.go

@@ -1,4 +1,4 @@
-package main
+package benchmarks
 
 import (
 	. "github.com/tendermint/go-common"