message: Add help suggestion on webpack failure
diff: @@ -122,7 +122,9 @@ fn write_wranglerjs_output(
  ) -> Result<(), failure::Error> {
  if output.has_errors() {
  message::user_error(output.get_errors().as_str());
  - failure::bail!("Webpack returned an error");
  + failure::bail!(
  + "webpack returned an error. You may be able to resolve this issue by running npm install."
  + );
  }
  bundle.write(output)?;
  