Update travis script to avoid using pre-release of cocoapods

.travis.yml

@@ -13,7 +13,7 @@ notifications:
 before_install:
     - env
     - locale
-    - gem install cocoapods --pre --no-rdoc --no-ri --no-document --quiet
+    - gem install cocoapods --no-rdoc --no-ri --no-document --quiet
     - gem install xcpretty --no-rdoc --no-ri --no-document --quiet
     - pod --version
     - pod setup --silent > /dev/null