Update suggested build type on troubleshoot msg

When an error occurs, user is suggested to disable
the `dev_build` but it suggests using `--dev-mode=False`
which should actually be `--dev-build=False`

jupyterlab/labapp.py

@@ -48,7 +48,7 @@
 If you are building via the `jupyter lab build` command, you can disable
 these options like so:
 
-jupyter lab build --dev-mode=False --minimize=False
+jupyter lab build --dev-build=False --minimize=False
 
 You can also disable these options for all JupyterLab builds by adding these
 lines to a Jupyter config file named `jupyter_config.py`: