allow Floats and other numerics in Plist

this change would allow to set, float values which are used to specify
the UIStatusBarTintParameters.
e.g.:
  app.info_plist["UIStatusBarTintParameters"] = {
     "UINavigationBar" => {
        "Style" => "UIBarStyleDefault", 
        "TintColor" => {
           "Green" => 68.0, 
           "Red"   => 220.0, 
           "Blue"  => 63.0
        }, 
        "Translucent" => true
     }
  }