set chrome path for travis CI explicitly

karma seems to be giving priority to a location where an old version is installed.

.travis.yml

@@ -24,5 +24,5 @@ install:
     # commit.
     - npm install && scripts/fetch-develop.deps.sh --depth 1
 script:
-    - npm run test
+    - CHROME_BIN='/usr/bin/google-chrome-stable' npm run test
     - npm run lint