Fix isNuclideDebuggingAvailable on iOS

Reviewed By: bnham

Differential Revision: D6567435

fbshipit-source-id: e8c4d8a3e02fe767f5a6871db61b21faf181cc43

Author: pakoito

React/Modules/RCTDevSettings.mm

@@ -42,6 +42,7 @@
 
 #if RCT_ENABLE_INSPECTOR
 #import "RCTInspectorDevServerHelper.h"
+#import <jschelpers/JSCWrapper.h>
 #endif
 
 #if RCT_DEV
@@ -255,7 +256,7 @@ - (id)settingForKey:(NSString *)key
 - (BOOL)isNuclideDebuggingAvailable
 {
 #if RCT_ENABLE_INSPECTOR
-  return true;
+  return facebook::react::isCustomJSCPtr(_bridge.jsContextRef);
 #else
   return false;
 #endif //RCT_ENABLE_INSPECTOR