Use Luarocks to install luacheck

Also remove worthless variable.

.github/workflows/check-release.yml

@@ -1,11 +1,15 @@
 on: [push, pull_request]
 name: Check & Release
+
 jobs:
   lint:
     runs-on: ubuntu-latest
+
     steps:
-      - uses: actions/checkout@master
-      - name: lint
-        uses: Roang-zero1/factorio-mod-luacheck@master
-        with:
-          luacheckrc_url: https://raw.githubusercontent.com/Uberi/Minetest-WorldEdit/master/.luacheckrc
+    - uses: actions/checkout@v1
+    - name: apt
+      run: sudo apt-get install -y luarocks
+    - name: luacheck install
+      run: luarocks install --local luacheck
+    - name: luacheck run
+      run: $HOME/.luarocks/bin/luacheck ./