Add branch filter for builds (#268)

Summary:
Nothing seems to run now, so let's try "trigger schedules" instead.
Pull Request resolved: https://github.com/facebook/flipper/pull/268

Reviewed By: priteshrnandgaonkar

Differential Revision: D9851086

Pulled By: passy

fbshipit-source-id: 8327e0f7b2a416541e8b531578ea813cc168ff66

.circleci/config.yml

@@ -25,8 +25,15 @@ workflows:
   build:
     jobs:
       - build
-      - release:
+
+  release:
+    triggers:
+      - schedules:
           filters:
+            branches:
+              - only: master
             tags:
               - only: /^v.*/
 
+    jobs:
+      - release