Fix client-go installation in Makefile

Makefile

@@ -33,9 +33,11 @@ cmd/hercules/plugin_template_source.go: cmd/hercules/plugin.template
 	cd cmd/hercules && go generate
 
 ${GOPATH}/src/gopkg.in/bblfsh/client-go.v2:
-	go get -d -v gopkg.in/bblfsh/client-go.v2/... && \
+	go get -d -v gopkg.in/bblfsh/client-go.v2/...
+
+${GOPATH}/pkg/*/gopkg.in/bblfsh/client-go.v2: ${GOPATH}/src/gopkg.in/bblfsh/client-go.v2
 	cd ${GOPATH}/src/gopkg.in/bblfsh/client-go.v2 && \
 	make dependencies
 
-${GOPATH}/bin/hercules${EXE}: *.go cmd/hercules/*.go rbtree/*.go yaml/*.go toposort/*.go pb/*.go ${GOPATH}/src/gopkg.in/bblfsh/client-go.v2 pb/pb.pb.go pb/pb_pb2.py cmd/hercules/plugin_template_source.go
+${GOPATH}/bin/hercules${EXE}: *.go cmd/hercules/*.go rbtree/*.go yaml/*.go toposort/*.go pb/*.go ${GOPATH}/pkg/*/gopkg.in/bblfsh/client-go.v2 pb/pb.pb.go pb/pb_pb2.py cmd/hercules/plugin_template_source.go
 	go get -ldflags "-X gopkg.in/src-d/hercules.v3.BinaryGitHash=$(shell git rev-parse HEAD)" gopkg.in/src-d/hercules.v3/cmd/hercules