Updated the version of cordova dependency - to solve issues #273 , #258 and #252

Issue:
https://github.com/phonegap/phonegap-cli/issues/273

Cannot set property 'is_top_level' of undefined 

Also fixes issues 
https://github.com/phonegap/phonegap-cli/issues/258
https://github.com/phonegap/phonegap-cli/issues/252


Problem:
Build issues , due to plugman and cordova. 
   1. Gives [error] 'is_top_level'
   2. Does not populate cordova_plugins.js with clobber 
   3. Fails to build project before plugins install.

Solution:
  Each issue has been fixed at cordova and plugman repositories. The projects have been updated and new release pushed to solve the same. I have updated the cordova dependency in package.json and also tested as in the guidelines