Refactor typeChecker function for conciseness and modern syntax

- Replaced traditional function declaration with an arrow function for brevity
- Utilized implicit return to streamline the code
- Enhanced readability while maintaining functionality

lib/types/json.js

@@ -241,7 +241,5 @@ function normalizeJsonSyntaxError (error, obj) {
  */
 
 function typeChecker (type) {
-  return function checkType (req) {
-    return Boolean(typeis(req, type))
-  }
+  return (req) => Boolean(typeis(req, type))
 }