Fixed typo.

Author: AnyhowStep

lib/lib.es5.d.ts

@@ -1486,7 +1486,7 @@ type ConstructorParameters<T extends new (...args: any) => any> = T extends new
 /**
  * Obtain the return type of a function type
  */
-type ReturnType<T extends (...args: never) => any> = T extends (...args: never) => infer R ? R : any;
+type ReturnType<T extends (...args: any) => any> = T extends (...args: never) => infer R ? R : any;
 
 /**
  * Obtain the return type of a constructor function type