chore: add @types/prettier package

Author: G-Rath

package.json

@@ -104,6 +104,7 @@
     "@types/dedent": "^0.7.0",
     "@types/jest": "^25.1.0",
     "@types/node": "^12.6.6",
+    "@types/prettier": "^1.19.0",
     "@typescript-eslint/eslint-plugin": "^2.5.0",
     "@typescript-eslint/parser": "^2.5.0",
     "babel-jest": "^25.2.0",