Fix Windows Nightly (#2225)

* Set nightly flag in bash shell for all OS

Author: seanpmorgan

.github/workflows/release.yml

@@ -51,6 +51,7 @@ jobs:
             const commit_details = await github.git.getCommit({owner: context.repo.owner, repo: context.repo.repo, commit_sha: context.sha});
             return commit_details.data.author.date
       - if: github.event_name == 'push'
+        shell: bash
         run: echo "NIGHTLY_FLAG=--nightly" >> $GITHUB_ENV
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v1