Add build path for BLS

.travis.yml

@@ -3,6 +3,9 @@ go:
   - master
 install:
   - export GOPATH=$HOME/gopath
+  - export CGO_CPPFLAGS="-I$GOPATH/src/github.com/harmony-one/bls/include -I$GOPATH/src/github.com/harmony-one/mcl/include"
+  - export CGO_LDFLAGS="-L$GOPATH/src/github.com/harmony-one/bls/lib -L$GOPATH/src/github.com/harmony-one/mcl/lib"
+  - export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$GOPATH/src/github.com/harmony-one/bls/lib
   - cd $HOME/gopath/src
   - cd github.com/harmony-one/harmony
   - go get -t -v ./...