pin casper to 1.1.0-beta5

to see if this fixes the shutdown test failure

.travis.yml

@@ -26,7 +26,7 @@ before_install:
     - nvm install 5.6
     - nvm use 5.6
     - npm upgrade -g npm
-    - 'if [[ $GROUP == js* ]]; then  npm install -g casperjs; fi'
+    - 'if [[ $GROUP == js* ]]; then  npm install -g casperjs@1.1.0-beta5; fi'
     - git clone --quiet --depth 1 https://github.com/minrk/travis-wheels travis-wheels
 
 install: