Fixes #77 (Fix crash on didFailNavigation)

Author: charafau

ios/Classes/FlutterWebviewPlugin.m

@@ -270,10 +270,7 @@ - (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigat
 }
 
 - (void)webView:(WKWebView *)webView didFailNavigation:(WKNavigation *)navigation withError:(NSError *)error {
-    id data = [FlutterError errorWithCode:[NSString stringWithFormat:@"%ld", error.code]
-                                  message:error.localizedDescription
-                                  details:error.localizedFailureReason];
-    [channel invokeMethod:@"onError" arguments:data];
+    [channel invokeMethod:@"onError" arguments:@{@"code": [NSString stringWithFormat:@"%ld", error.code], @"error": error.localizedDescription}];
 }
 
 - (void)webView:(WKWebView *)webView decidePolicyForNavigationResponse:(WKNavigationResponse *)navigationResponse decisionHandler:(void (^)(WKNavigationResponsePolicy))decisionHandler {
@@ -292,4 +289,4 @@ - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
     }
 }
 
-@end
+@end