Update gem install command for cocoapods gem in travis.yml

Author: hamchapman

.travis.yml

@@ -29,7 +29,7 @@ before_install:
       echo Carthage not installed. Installing using homebrew;
       brew install carthage;
     fi
-  - gem install cocoapods -v 1.0.0.beta.2
+  - gem install cocoapods -v 1.0.0.beta.4
 install:
   - pod _1.0.0.beta.4_ install
 script: