add support for Cordova 3.5.x (#5)

https://github.com/Telerik-Verified-Plugins/WKWebView/issues/5

I investigated why this was not working with Cordova 3.5 and found that a new js to native bridge was added in Cordova 3.6.0 (?) to support WKWebView.  Here's the commit: https://github.com/apache/cordova-js/commit/0329464c7bb538cc469dc965e28f5801ea14422f

I read some discussion in one of the issues as well as the readme (deviceready never fires with 3.5.0 due to a currently unknown reason) regarding 3.5.0 and thought you might be interested in a trying this fix out.