Use nimbella dev branch for go proxy. (#102)

core/python3ActionLoop/Dockerfile

diff --git a/core/python3ActionLoop/Dockerfile b/core/python3ActionLoop/Dockerfile
index 5e882b2..da898f3 100644
--- a/core/python3ActionLoop/Dockerfile
+++ b/core/python3ActionLoop/Dockerfile
@@ -16,6 +16,7 @@
 #
 # build go proxy from source
 FROM golang:1.15 AS builder_source
+
 ARG GO_PROXY_GITHUB_USER=apache
 ARG GO_PROXY_GITHUB_BRANCH=master
 RUN git clone --branch ${GO_PROXY_GITHUB_BRANCH} \
@@ -33,6 +34,8 @@
   && GO111MODULE=on go build -o /bin/proxy
 
 FROM python:3.7-buster
+
+# select the builder to use
 ARG GO_PROXY_BUILD_FROM=release
 
 # Install common modules for python
@@ -66,4 +69,3 @@
 ENV OW_COMPILER=/bin/compile
 
 ENTRYPOINT ["/bin/proxy"]
-