run CI on pull requests (#22)

* run CI on pull requests

* use node 12

Author: dschaller

.github/workflows/blank.yml

@@ -1,13 +1,24 @@
 name: CI
-
-on: [push]
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
+    paths-ignore:
+    - '.gitignore'
+    - '.npmignore'
+    - '*.md'
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
-
     steps:
+    - name: Install Node
+      uses: actions/setup-node@v1
+      with:
+        node-version: '12.x'
     - uses: actions/checkout@v1
     - name: Run build
       run: npm install && npm run build