[iOS] Add requiresMainQueueSetup

Closes #63

Author: christopherdro

ios/RNHTMLtoPDF/RNHTMLtoPDF.m

@@ -48,6 +48,11 @@ @implementation RNHTMLtoPDF {
 
 RCT_EXPORT_MODULE();
 
++ (BOOL)requiresMainQueueSetup
+{
+    return YES;
+}
+
 @synthesize bridge = _bridge;
 
 - (instancetype)init