Update comment on ImportStatement#to_import_string
Update comment on ImportStatement#to_import_string

As @trotzig pointed out, when I changed this method to return array, I
didn't update the wording here.

lencioni/import-js,lencioni/import-js,Galooshi/import-js,lencioni/import-js,trotzig/import-js,trotzig/import-js,trotzig/import-js