add typecheck command

Author: mmalfertheiner

package.json

@@ -17,6 +17,7 @@
     "build": "tsc",
     "lint": "eslint --ext js,ts,tsx src",
     "lint:fix": "npm run lint -- --fix",
+    "typecheck": "tsc --noEmit",
     "test": "jest --config jest.config.js --passWithNoTests",
     "prepare": "npm run build",
     "prepublishOnly": "npm run test && npm run lint",