Fix code of insufficient permissions error

Signed-off-by: trivernis <trivernis@protonmail.com>

src/errors/PermissionError.ts

@@ -2,6 +2,6 @@ import { ApolloError } from 'apollo-server-express';
 
 export class PermissionError extends ApolloError {
     constructor () {
-        super('Insufficient permissions.', 'INSUFFICIENT_PERMISSION');
+        super('Insufficient permissions.', 'INSUFFICIENT_PERMISSIONS');
     }
 }