Add dependabot tidy github workflow (#94)

.github/workflows/dependabot.yml

@@ -0,0 +1,28 @@
+name: Dependabot-Tidier
+on:
+  pull_request:
+    types: [ labeled ]
+
+jobs:
+  mod_tidier:
+    if: ${{ contains(github.event.pull_request.labels.*.name, 'dependencies') }}
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        ref: ${{ github.head_ref }}
+    - uses: actions/setup-go@v2
+      with:
+        go-version: '^1.14.0'
+    - uses: evantorrie/mott-the-tidier@v1-beta
+      id: modtidy
+      with:
+        gomods: '**/go.mod'
+        gosum_only: true
+    - uses: stefanzweifel/git-auto-commit-action@v4
+      id: autocommit
+      with:
+        commit_message: Auto-fix go.sum changes in dependent modules
+    - name: changes
+      run: |
+        echo "Changes detected: ${{ steps.autocommit.outputs.changes_detected }}"