Add bibclen fixer support

Closes #1910

test/fixers/test_rufo_fixer_callback.vader

@@ -4,9 +4,7 @@ Before:
   " Use an invalid global executable, so we don't match it.
   let g:ale_ruby_rufo_executable = 'xxxinvalid'
 
-  call ale#test#SetDirectory('/testplugin/test/fixers')
-  silent cd ..
-  silent cd command_callback
+  call ale#test#SetDirectory('/testplugin/test/command_callback')
   let g:dir = getcwd()
 
 After: