Fix bugs in Make pip-install action

[yds05]

Issue:

1. If use already installed an older node(<10.8), pip install will failed because yarn build will pick the older version node.
2. pip-install action doesn't create examples folder under $HOME.

[Crysple]

thanks for fixs and it seems unnecessary to export yarn cuz the $(YARN) defined at the beginning of Makefile has explicitly to specify the 'yarn'. Otherwise this variable can be deleted and just 'yarn' is used