Fix pipelines push script

bitbucket-pipelines.yml

@@ -15,7 +15,7 @@ pipelines:
           deployment: staging   # set to test, staging or production
           # trigger: manual  # uncomment to have a manual step
           script:
-            - git push https://heroku:$HEROKU_API_KEY@git.heroku.com/$HEROKU_APP_NAME.git master
+            - git push https://heroku:$HEROKU_API_KEY@git.heroku.com/$HEROKU_APP_NAME.git HEAD:master
     develop:
       - step:
           # set HEROKU_API_KEY and HEROKU_APP_NAME environment variables
@@ -24,5 +24,5 @@ pipelines:
           deployment: test   # set to test, staging or production
               # trigger: manual  # uncomment to have a manual step
           script:
-            - git push https://heroku:$HEROKU_API_KEY@git.heroku.com/$HEROKU_APP_NAME_TEST.git master
+            - git push https://heroku:$HEROKU_API_KEY@git.heroku.com/$HEROKU_APP_NAME_TEST.git HEAD:master