Adds workflow for code linting

.github/workflows/lint.yaml

@@ -0,0 +1,28 @@
+# Run flutter linting checks
+
+name: linting
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v1
+        with:
+          java-version: '12.x'
+      - uses: subosito/flutter-action@v1
+        with:
+          flutter-version: '2.2.3'
+      - run: flutter pub get
+      - run: flutter analyze
+