Upgrade to GitHub-native Dependabot

.github/dependabot.yml

@@ -0,0 +1,17 @@
+version: 2
+updates:
+- package-ecosystem: npm
+  directory: "/"
+  schedule:
+    interval: monthly
+    time: "20:00"
+    timezone: Asia/Tokyo
+  open-pull-requests-limit: 10
+  ignore:
+  - dependency-name: textlint
+    versions:
+    - 11.7.7
+    - 11.8.1
+  - dependency-name: textlint-rule-no-dropping-the-ra
+    versions:
+    - 2.0.0