add .github/workflows/automerge.yml (#140)

.github/workflows/automerge.yml

+# File managed by web3-bot. DO NOT EDIT.
+# See https://github.com/protocol/.github/ for details.
+
+# Automatically merge pull requests opened by web3-bot, as soon as (and only if) all tests pass.
+# This reduces the friction associated with updating with our workflows.
+
+on: [ pull_request ]
+
+jobs:
+  automerge:
+    if: github.event.pull_request.user.login == 'web3-bot'
+    runs-on: ubuntu-latest
+    steps:
+    - name: Wait on tests
+      uses: lewagon/wait-on-check-action@bafe56a6863672c681c3cf671f5e10b20abf2eaa # v0.2
+      with:
+        ref: ${{ github.event.pull_request.head.sha }}
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        wait-interval: 10
+        running-workflow-name: 'automerge' # the name of this job
+    - name: Merge PR
+      uses: pascalgn/automerge-action@741c311a47881be9625932b0a0de1b0937aab1ae # v0.13.1
+      env:
+        GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
+        MERGE_LABELS: ""
+        MERGE_METHOD: "squash"
+        MERGE_DELETE_BRANCH: true