chore: add shellcheck to github actions (haoel#65)

Author: Dup4

.github/workflows/shellcheck.yml

@@ -0,0 +1,17 @@
+name: 'Shellcheck'
+
+on:
+  push:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  shellcheck:
+    name: Shellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Run ShellCheck
+        uses: ludeeus/action-shellcheck@master