message: Update build_mozc_in_docker.md
diff: @@ -40,7 +40,7 @@ bazel build package --config oss_linux -c opt
  ```
  `package` is an alias to build `server:mozc_server`, `gui/tool:mozc_tool`,
  -`renderer:mozc_renderer` and `ibus:ibus_mozc`.
  +`renderer:mozc_renderer`, `ibus:ibus_mozc` and `emacs:mozc_emacs_helper`.
  Unittests can be executed as follows.
  