tweak npm version check done for browser builds
tweak npm version check done for browser builds

shouldn't warn about custom installs. also allow disabling
completely via

   :js-options {:check-versions false}

thheller/shadow-devtools,thheller/shadow-cljs,thheller/shadow-cljs,thheller/shadow-cljs,thheller/shadow-devtools,thheller/shadow-devtools,thheller/shadow-cljs,thheller/shadow-devtools