Fix typo in GCM::Notification

lib/pushmeup/gcm/notification.rb

@@ -18,15 +18,15 @@ def device_tokens=(tokens)
       elsif tokens.is_a?(String)
         @device_tokens = [tokens]
       else
-        raise "device_tokens needs to be either a hash or string"
+        raise "device_tokens needs to be either a Hash or String"
       end
     end
 
     def data=(data)
       if data.is_a?(Hash)
         @data = data
       else
-        raise "data parameter must be the tpe of Hash"
+        raise "data parameter must be the type of Hash"
       end
     end
 
@@ -52,4 +52,4 @@ def ==(that)
     end
 
   end
-end
+end