Change JSONRepresentation to JSONString for PhoneGap 1.3 #17

README.md indicates that the name of the header file was changed JSON.h to JSONKit.h in PhoneGap 1.3. In addition, [resultSet JSONString] must be used in place of [resultSet JSONRepresentation] in Plugins/PGSQLitePlugin.m. I will post a pull request with this fix in README.md. Please bear with me that this is my first time using github and I am also just starting using Objective-C.