Update build-lambda-zip workflow (#267)

Update build-lambda-zip workflow

* run on push to master
* explicit go get @master

Author: bmoffatt

.github/workflows/build-lambda-zip.yml

@@ -1,6 +1,8 @@
 name: go get build-lambda-zip 
 on:
   push:
+    branches: 
+      - master
   schedule:
     - cron: "7 7 * * *"
 
@@ -24,4 +26,4 @@ jobs:
           GO111MODULE: on
         run: |
           go env
-          go get -u github.com/aws/aws-lambda-go/cmd/build-lambda-zip
+          go get -u github.com/aws/aws-lambda-go/cmd/build-lambda-zip@master