chore: update .travis.yml

Author: achingbrain

.travis.yml

@@ -57,7 +57,7 @@ jobs:
     - stage: release
       name: release rc
       script:
-        - echo "//registry.npmjs.org/:_authToken=\${NPM_TOKEN}" > ../.npmrc
+        - echo "//registry.npmjs.org/:_authToken=$NPM_TOKEN" > ../.npmrc
         - npm run release:rc -- --yes
 
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