[chore] Update function lock file and modify travis to use yarn for functions

Author: seblucas

.travis.yml

@@ -20,7 +20,7 @@ cache: yarn
 
 before_deploy:
   - zip -r firebase-sensor.zip dist
-  - cd functions && npm install && cd ..
+  - cd functions && yarn install --pure-lockfile --ignore-engines && cd ..
 
 deploy:
   - provider: releases