vim/vint: show policy name

So that I can find the relevant information in the vint
linting policy summary and policies can be easily configured
https://github.com/Vimjas/vint/wiki/Vint-linting-policy-summary

Before this change an example warning message appears as:

    autocmd should execute in an augroup or execute with a group (see :help :autocmd)

After this change the same example appears as:

    ProhibitAutocmdWithNoGroup - autocmd should execute in an augroup or execute with a group (see :help :autocmd)

test/command_callback/test_vint_command_callback.vader

@@ -1,7 +1,7 @@
 Before:
   call ale#assert#SetUpLinterTest('vim', 'vint')
   let b:command_tail = (has('nvim') ? ' --enable-neovim' : '')
-  \ . ' -f "{file_path}:{line_number}:{column_number}: {severity}: {description} (see {reference})" %t'
+  \ . ' -f "{file_path}:{line_number}:{column_number}: {severity}: {policy_name} - {description} (see {reference})" %t'
 
 After:
   unlet! b:bin_dir