webpack-dev-middleware: Fix lint (#22700)

types/webpack-dev-middleware/v1/index.d.ts

@@ -54,4 +54,4 @@ declare namespace WebpackDevMiddleware {
 		getFilenameFromUrl: (url: string) => string | false;
 		fileSystem: MemoryFileSystem;
 	}
-}
+}

types/webpack-dev-middleware/v1/webpack-dev-middleware-tests.ts

@@ -47,4 +47,4 @@ fs.mkdirpSync('foo');
 let filename = webpackDevMiddlewareInstance.getFilenameFromUrl('url');
 if (filename !== false) {
 	filename = filename.substr(0);
-}
+}