Use gh actions for linting

.github/workflows/lint.yml

@@ -0,0 +1,44 @@
+name: lint
+
+on:
+  # Trigger the workflow on push or pull request,
+  # but only for the master branch
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  syntax:
+    name: flake8 syntax
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.7
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install flake8
+      - name: lint
+        run: |
+          flake8 fluent-syntax/fluent
+
+  runtime:
+    name: flake8 runtime
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.7
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install flake8
+      - name: lint
+        run: |
+          flake8 fluent-runtime/fluent