Fix Docker build (#24)

Correct path to go runtime
diff --git a/core/ruby2.6ActionLoop/Dockerfile b/core/ruby2.6ActionLoop/Dockerfile
index 814608e..8101032 100644
--- a/core/ruby2.6ActionLoop/Dockerfile
+++ b/core/ruby2.6ActionLoop/Dockerfile
@@ -15,10 +15,10 @@
 # limitations under the License.
 #
 FROM golang:1.11 as builder
-ENV PROXY_SOURCE=https://github.com/apache/incubator-openwhisk-runtime-go/archive/golang1.11@v1.13.0-incubating.tar.gz
+ENV PROXY_SOURCE=https://github.com/apache/incubator-openwhisk-runtime-go/archive/golang1.11@1.13.0-incubating.tar.gz
 RUN curl -L "$PROXY_SOURCE" | tar xzf - \
   && mkdir -p src/github.com/apache \
-  && mv incubator-openwhisk-runtime-go-golang1.11-v1.13.0-incubating \
+  && mv incubator-openwhisk-runtime-go-golang1.11-1.13.0-incubating \
      src/github.com/apache/incubator-openwhisk-runtime-go \
   && cd src/github.com/apache/incubator-openwhisk-runtime-go/main \
   && CGO_ENABLED=0 go build -o /bin/proxy