Use rails compiler plugin for :make

Note that previously, use of a compiler plugin was limited to systems
with Projectionist present, but now it's enabled for all users.

autoload/rails.vim

@@ -4821,6 +4821,11 @@ function! rails#buffer_setup() abort
       endif
     endif
   endif
+
+  compiler rails
+  let &l:makeprg = self.app().rake_command('static')
+  let &l:errorformat .= ',chdir '.escape(self.app().path(), ',')
+
   if self.type_name('test', 'spec', 'cucumber')
     call self.setvar('dispatch', ':Runner')
   elseif self.name() ==# 'Rakefile'

plugin/rails.vim

@@ -82,7 +82,7 @@ augroup railsPluginDetect
   autocmd User ProjectionistDetect
         \ if RailsDetect(get(g:, 'projectionist_file', '')) |
         \   call projectionist#append(b:rails_root,
-        \     {'*': {'make': split(rails#app().rake_command('static'))}}) |
+        \     {'*': {}}) |
         \ endif
 augroup END