allow custom command for installing npm packages from deps.cljs
allow custom command for installing npm packages from deps.cljs

fixes #404

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