[mod] simple theme - add ESLint

[1] https://eslint.org/
[2] https://eslint.org/docs/user-guide/configuring/
[3] https://eslint.org/docs/user-guide/command-line-interface

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

manage

@@ -665,6 +665,8 @@ themes.oscar() {
 themes.simple() {
     build_msg GRUNT "theme: simple"
     npm --prefix searx/static/themes/simple run build
+    # just report eslint issues but do not break the build (--force)
+    npm --prefix searx/static/themes/simple run eslint --force
     dump_return $?
 }