Bump Bazel version to 3.1.0
Bump Bazel version to 3.1.0

Change-Id: Ia2518fcbf53ba42bba92667d74b353bc71846319

GerritCodeReview/plugins_delete-project,GerritCodeReview/plugins_delete-project,GerritCodeReview/plugins_delete-project,GerritCodeReview/plugins_delete-project