fix(iOS WKWebView): fixed local html files loading on real devices (#403)

ios/RNCWKWebView.m

     [_webView loadHTMLString:@"" baseURL:nil];
     return;
   }
-  [_webView loadRequest:request];
+  if (request.URL.host) {
+    [_webView loadRequest:request];
+  }
+  else {
+    [_webView loadFileURL:request.URL allowingReadAccessToURL:request.URL];
+  }
+
 }
 
 -(void)setHideKeyboardAccessoryView:(BOOL)hideKeyboardAccessoryView