Correctly find callInvite to cancel (#198)

* Correctly find callInvite to cancel

I'm a novice at iOS development, but in my attempt to copy this QuickStart implementation into hoxfon/react-native-twilio-programmable-voice#138 I needed to make this change to get the cancel to work correctly.

I wanted to share this change with you, but I have not tested it in this repo myself. Please confirm and merge if it is an issue.

* Updated key name to uuid

Author: lonnylot

ObjcVoiceQuickstart/ViewController.m

@@ -356,9 +356,10 @@ - (void)cancelledCallInviteReceived:(TVOCancelledCallInvite *)cancelledCallInvit
     NSLog(@"cancelledCallInviteReceived:");
 
     TVOCallInvite *callInvite;
-    for (TVOCallInvite *invite in self.activeCallInvites) {
-        if ([cancelledCallInvite.callSid isEqualToString:invite.callSid]) {
-            callInvite = invite;
+    for (NSString *uuid in self.activeCallInvites) {
+        TVOCallInvite *activeCallInvite = [self.activeCallInvites objectForKey:uuid];
+        if ([cancelledCallInvite.callSid isEqualToString:activeCallInvite.callSid]) {
+            callInvite = activeCallInvite;
             break;
         }
     }