Missing RouteMatchInterface import

Problem/Motivation

Module version 1.1.2 breaks site because RouteMatchInterface import is missing in custom_500_error.module file.

Steps to reproduce

1. Install or upgrade module.
2. Open front page and see the following Type error:

TypeError: custom_500_error_help(): Argument #2 ($route_match) must be of type RouteMatchInterface, Drupal\Core\Routing\CurrentRouteMatch given

Proposed resolution

Add missing import.