Fix Travis Tests (#96)

* Bump testing service

* Add caching of browsers to speed up build times

* Add a comment for caching directory

Author: Matt Gaunt

.travis.yml

@@ -1,6 +1,12 @@
 dist: trusty
 language: php
 
+ # Downloaded browsers will be cached in selenium-assistant by
+ # web-push-testing-service. Caching will speed up build time.
+cache:
+  directories:
+    - ~/.selenium-assistant
+
 php:
   - 5.6
   - hhvm
@@ -14,7 +20,7 @@ before_install:
   - nvm install node
 
 install:
-  - npm install [email protected].0 -g
+  - npm install [email protected].1 -g
 
 before_script:
   - composer install --prefer-source -n