Upgrade to GitHub-native Dependabot (#44)

* Upgrade to GitHub-native Dependabot

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Phil Chen <[email protected]>

Author: dependabot-preview[bot]

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+- package-ecosystem: mix
+  directory: "/"
+  schedule:
+    interval: daily
+  open-pull-requests-limit: 1
+  assignees:
+  - fahchen
+  versioning-strategy: lockfile-only