use released sources to build actionloop proxy (#56)

diff --git a/core/php7.3Action/Dockerfile b/core/php7.3Action/Dockerfile
index 1b203b1..67fcd5d 100644
--- a/core/php7.3Action/Dockerfile
+++ b/core/php7.3Action/Dockerfile
@@ -15,8 +15,14 @@
 # limitations under the License.
 #
 
-FROM openwhisk/actionloop:42fd5e6 as builder
-
+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
+RUN curl -L "$PROXY_SOURCE" | tar xzf - \
+  && mkdir -p src/github.com/apache \
+  && mv incubator-openwhisk-runtime-go-golang1.11-v1.13.0-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
 FROM php:7.3.3-cli-stretch
 
 # install dependencies