v1.9 tag

Release v1.8

Upgrade pai restful API (microsoft#2722)

Add torch requirement to nasbench201 (microsoft#2663)

v1.6 release note (microsoft#2491)

Merge pull request microsoft#2282 from microsoft/master

release v1.4

NNI release for v1.3

Release note (microsoft#1809)

Fix package installation in virtualenv and conda (microsoft#1640)

* Refactor package installation

* reformat docstring

* fix issue when user is root