add check:eslint step to typecheck the eslint-rules directory

eslint-rules/tsconfig.json

@@ -0,0 +1,11 @@
+{
+  "compilerOptions": {
+    "allowJs": true,
+    "checkJs": true,
+    "noEmit": true,
+    "target": "es2015",
+    "skipLibCheck": true,
+    "moduleResolution": "node"
+  },
+  "include": ["*.js", "test/*.js"]
+}

package.json

@@ -6,6 +6,7 @@
   "description": "GitHub Desktop build dependencies",
   "scripts": {
     "cli": "ts-node --require ./app/test/globals.ts --require ./app/src/cli/dev-commands-global.ts app/src/cli/main.ts",
+    "check:eslint": "tsc -P eslint-rules/",
     "test:eslint": "jest eslint-rules/tests/*.test.js",
     "test:integration": "cross-env TEST_ENV=1 ELECTRON_NO_ATTACH_CONSOLE=1 xvfb-maybe --auto-servernum -- jest --testLocationInResults --config ./app/jest.integration.config.js",
     "test:unit": "cross-env ELECTRON_RUN_AS_NODE=1 ./node_modules/.bin/electron ./node_modules/jest/bin/jest --detectOpenHandles --silent --testLocationInResults --config ./app/jest.unit.config.js",