chore(GHActions): replace with dependabot (#1348)

* chore(GHActions): replace with dependabot

* chore(GHActions): remove tidy.yml due to deprecation

.github/dependabot.yml

@@ -0,0 +1,12 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://help.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "gomod" # See documentation for possible values
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"
+    target-branch: "master"

.github/workflows/tidy.yml

@@ -1,22 +0,0 @@
-name: go-mod-tidy-pr
-
-on:
-  schedule:
-    - cron: "0 0 * * 1" # Weekly build
-
-jobs:
-  go-mod-tidy-pr:
-    name: go-mod-tidy-pr
-
-    runs-on: ubuntu-latest
-
-    steps:
-      - uses: actions/checkout@v2
-
-      - name: Run go-mod-tidy-pr
-        uses: sue445/go-mod-tidy-pr@master
-        with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          git_user_name: kotakanbe
-          git_user_email: kotakanbe@gmail.com
-          go_version: 1.16.x