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.

.eslintrc.js

@@ -1,6 +1,12 @@
 module.exports = {
+    plugins: [
+        "matrix-org",
+    ],
+    extends: [
+        "plugin:matrix-org/javascript",
+    ],
     parserOptions: {
-        ecmaVersion: 8,
+        ecmaVersion: 2021,
     },
     env: {
         es6: true,
@@ -8,12 +14,7 @@ module.exports = {
         // we also have some browser code (ie. the preload script)
         browser: true,
     },
-    extends: ["matrix-org"],
     rules: {
-        // js-sdk uses a babel rule which we can't use because we
-        // don't use babel, so remove it & put the original back
-        "babel/no-invalid-this": "off",
-        "no-invalid-this": "error",
         "quotes": "off",
         "indent": "off",
         "prefer-promise-reject-errors": "off",

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": "7.18.0",
-    "eslint-config-matrix-org": "^0.1.2",
+    "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",