Add GitHub workflow for JavaScript building

extensions/markdown/.github/workflows/build.yml

@@ -0,0 +1,17 @@
+name: Build JavaScript assets
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@master
+      - uses: flarum/action-build@master
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+

extensions/markdown/.travis.yml

@@ -1,13 +0,0 @@
-language: generic
-
-cache:
-  directories:
-    - $HOME/.npm
-
-jobs:
-  include:
-    - stage: build
-      if: branch = master AND type = push
-      script: curl -s https://raw.githubusercontent.com/flarum/core/master/.travis/build.sh | bash -s -
-        -k $encrypted_fa711d174b0b_key
-        -i $encrypted_fa711d174b0b_iv