fix linting, add PR checks

.github/workflows/checks.yml

@@ -0,0 +1,22 @@
+name: Checks
+on: [push, pull_request]
+
+jobs:
+  lint:
+    name: Linting
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest]
+        node-version: [12.x]
+      fail-fast: true
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{matrix.node-version}}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{matrix.node-version}}
+      - name: Install modules
+        run: yarn install --frozen-lockfile
+      - name: Run ESLint
+        run: yarn lint

.prettierrc.js

@@ -1,3 +1,4 @@
 module.exports = {
   ...require('@joystream/prettier-config'),
+  printWidth: 120
 }

package.json

@@ -55,6 +55,6 @@
     "typescript": "^4.0.3"
   },
   "engines": {
-    "node": "^12.13.0"
+    "node": ">=12"
   }
 }