Migrate to eslint-plugin-matrix-org

Switch to the new linting package. It offers a new shared config for native
JavaScript, which this package targets.

package.json

@@ -47,8 +47,8 @@
     "electron-builder-squirrel-windows": "22.10.5",
     "electron-devtools-installer": "^3.1.1",
     "electron-notarize": "^1.0.0",
-    "eslint": "7.3.1",
-    "eslint-config-matrix-org": "^0.1.2",
+    "eslint": "7.18.0",
+    "eslint-plugin-matrix-org": "github:matrix-org/eslint-plugin-matrix-org#main",
     "find-npm-prefix": "^1.0.2",
     "fs-extra": "^8.1.0",
     "glob": "^7.1.6",