Merge pull request react-native-webrtc#24 from jitensuthar/master

Patched issue where RNCallKeep wouldn't execute properly if app is re…

Author: manuquentin

ios/RNCallKeep/RNCallKeep.m

@@ -58,6 +58,10 @@ - (void)dealloc
     NSLog(@"[RNCallKeep][dealloc]");
 #endif
     [[NSNotificationCenter defaultCenter] removeObserver:self];
+
+    if (self.callKeepProvider != nil) {
+        [self.callKeepProvider invalidate];
+    }
 }
 
 // Override method of RCTEventEmitter