Add workflow to update Pipfile.lock weekly (#1542)

* Create workflow to update the Pipfile.lock weekly

* Update-pipfile: Also install wheel

* Install wheel in different step

* Pipfile: Only lock major versions

Assumes Semantic Versioning, and only sets the major versions of all packages

* Run update-pipfile on changes in pipfile and use tensorflow

Move from tensorflow-gpu to tensorflow, an excelent test for this PR

* [create-pull-request] automated change

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

.github/workflows/update-pipfile.yml

@@ -0,0 +1,25 @@
+name: "Update Pipfile.lock"
+on:
+  schedule:
+    - cron: '00 08 * * 1' # Every monday on 08:00 UTC
+  push:
+    paths:
+    - 'Pipfile'
+
+jobs:
+  piplock:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-python@v2
+    - run: pip install wheel
+    - run: pip install pipenv
+    - run: pipenv lock --requirements
+    - uses: actions/upload-artifact@v2
+      with:
+        name: "Pipfile lock"
+        path: Pipfile.lock
+    - uses: peter-evans/create-pull-request@v2
+      with:
+        title: "Update Pipfile.lock (dependencies)"
+        branch: update-pipfile