Update sql.md

id converted to a number which is at findOne method because it shows error like 
`(property) id?: number | FindOperator<number>
Type 'string' is not assignable to type 'number | FindOperator<number>'.ts(2322)`

also, id is the number at the given example
https://github.com/nestjs/nest/blob/master/sample/05-sql-typeorm/src/users/users.service.ts#L26

Author: ylcnfrht

content/techniques/sql.md

@@ -180,7 +180,7 @@ export class UsersService {
     return this.usersRepository.find();
   }
 
-  findOne(id: string): Promise<User> {
+  findOne(id: number): Promise<User> {
     return this.usersRepository.findOneBy({ id });
   }