change the RobolectricPlugin because getRuntimeJarList has been deprecat...

this pull request resolve the problem after update to gradle 11 (this is mandatory on new android Studio 0.6). I dont upload the wrapper version because I believe that it's out of scope of the bug. 

The change it's update the versions and use bootclasspath instead of deprecated getRuntimeJarList
Uhmm I think that it's not necessary, sorry for that.