Make release stage conditional by branch

If the branch isn't a release branch, don't even try to do the release stage.  This should speed up PR tests.

.travis.yml

@@ -29,15 +29,13 @@ jobs:
       - git config --global user.name $(git log --pretty=format:"%an" -n1)
       deploy:
       - provider: npm
-        "on":
-          all_branches: true
-          condition: $RELEASE_BRANCHES =~ $TRAVIS_BRANCH
         skip_cleanup: true
         email: $NPM_EMAIL
         api_key: $NPM_TOKEN
       - provider: script
-        "on":
-          all_branches: true
-          condition: $RELEASE_BRANCHES =~ $TRAVIS_BRANCH
         skip_cleanup: true
         script: npm run --silent deploy -- -x -r $GH_PAGES_REPO
+stages:
+- test
+- name: release
+  if: branch in (master, develop)