Fix usage of NativeEventEmitter

ios/CodePush/CodePush.m

@@ -26,6 +26,9 @@ RCT_EXPORT_MODULE()
 
 #pragma mark - Private constants
 
+// These constants represent emitted events
+static NSString *const DownloadProgressEvent = @"CodePushDownloadProgress";
+
 // These constants represent valid deployment statuses
 static NSString *const DeploymentFailed = @"DeploymentFailed";
 static NSString *const DeploymentSucceeded = @"DeploymentSucceeded";
@@ -296,7 +299,7 @@ static NSString *bundleResourceSubdirectory = nil;
 
 - (void)dispatchDownloadProgressEvent {
   // Notify the script-side about the progress
-  [self sendEventWithName:@"CodePushDownloadProgress"
+  [self sendEventWithName:DownloadProgressEvent
                      body:@{
                        @"totalBytes" : [NSNumber
                            numberWithLongLong:_latestExpectedContentLength],
@@ -537,6 +540,10 @@ static NSString *bundleResourceSubdirectory = nil;
     [preferences synchronize];
 }
 
+- (NSArray<NSString *> *)supportedEvents {
+    return @[DownloadProgressEvent];
+}
+
 #pragma mark - Application lifecycle event handlers
 
 // These two handlers will only be registered when there is