build,travis: don't fail on WARNING

OpenWrt build now outputs WARNING on dependencies issues, for exemple
"WARNING: Makefile 'package/feeds/packages/coova-chilli/Makefile' has a dependency on 'libmatrixssl', which does not exist"

Relax the check for now

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

.travis_do.sh

@@ -113,8 +113,8 @@ EOF
 		pkg_name=$(echo "$pkg_dir" | awk -F/ '{ print $NF }')
 		echo_blue "=== $pkg_name: Starting quick tests"
 
-		exec_status 'WARNING|ERROR' make "package/$pkg_name/download" V=s || RET=1
-		exec_status 'WARNING|ERROR' make "package/$pkg_name/check" V=s || RET=1
+		exec_status '^ERROR' make "package/$pkg_name/download" V=s || RET=1
+		exec_status '^ERROR' make "package/$pkg_name/check" V=s || RET=1
 
 		echo_blue "=== $pkg_name: quick tests done"
 	done