message: Fix child process issue on web
  Refs
diff: import { VimError, ErrorCode } from '../error';
  -import { exec } from '../util/child_process';
  import { configuration } from '../configuration/configuration';
  class ExternalCommand {
  @@ -48,6 +47,8 @@ class ExternalCommand {
  };
  try {
  + const exec = (await import('../util/child_process')).exec;
  +
  const promise = exec(command, options);
  const process = promise.child;
  