Improve description for lexicographicSortSchema (#2412)

Replicates graphql-python/graphql-core@c61c65d

Author: IvanGoncharov

src/utilities/lexicographicSortSchema.d.ts

@@ -2,5 +2,7 @@ import { GraphQLSchema } from '../type/schema';
 
 /**
  * Sort GraphQLSchema.
+ *
+ * This function returns a sorted copy of the given GraphQLSchema.
  */
 export function lexicographicSortSchema(schema: GraphQLSchema): GraphQLSchema;

src/utilities/lexicographicSortSchema.js

@@ -31,6 +31,8 @@ import {
 
 /**
  * Sort GraphQLSchema.
+ *
+ * This function returns a sorted copy of the given GraphQLSchema.
  */
 export function lexicographicSortSchema(schema: GraphQLSchema): GraphQLSchema {
   const schemaConfig = schema.toConfig();