Fix importing NProgress
Fix importing NProgress

On case-sensitive operating systems, we have this error:
ERROR in ./assets/themes/concrete/js/main.js
Module not found: Error: Can't resolve 'NProgress'

Let's fix this

hissy/concrete5,mainio/concrete5,MrKarlDilkington/concrete5,concrete5/concrete5,haeflimi/concrete5,concrete5/concrete5,hissy/concrete5,mlocati/concrete5,jaromirdalecky/concrete5,concrete5/concrete5,haeflimi/concrete5,olsgreen/concrete5,hissy/concrete5,hissy/concrete5,mainio/concrete5,haeflimi/concrete5,mlocati/concrete5,mlocati/concrete5,deek87/concrete5,olsgreen/concrete5,mainio/concrete5,deek87/concrete5,deek87/concrete5,jaromirdalecky/concrete5,MrKarlDilkington/concrete5,haeflimi/concrete5,biplobice/concrete5,jaromirdalecky/concrete5,biplobice/concrete5,deek87/concrete5,biplobice/concrete5,mlocati/concrete5,biplobice/concrete5,olsgreen/concrete5,jaromirdalecky/concrete5,concrete5/concrete5,MrKarlDilkington/concrete5