Log errors during format to the console.

This stops the debugger breaking when this happens - it's really common
if you have compile errors.

src/providers/dart_formatting_edit_provider.ts

@@ -23,7 +23,7 @@ export class DartFormattingEditProvider implements DocumentFormattingEditProvide
 					resolve(null);
 				else
 					resolve(resp.edits.map(e => this.convertData(document, e)));
-			});
+			}, e => console.warn(e.message));
 		});
 	}