chore: update travis.yml

Author: achingbrain

.travis.yml

@@ -63,7 +63,7 @@ jobs:
     - stage: release
       name: release rc
       script:
-        - echo "//registry.npmjs.org/:_authToken=$NPM_TOKEN" > .npmrc
+        - echo "//registry.npmjs.org/:_authToken=\${NPM_TOKEN}" > .npmrc
         - npm whoami
         - npm run release:rc -- --yes