fix: unsupported usage (#53)

Author: BBboy01

lua/guard-collection/linter/shellcheck.lua

@@ -1,7 +1,6 @@
 return {
   cmd = 'shellcheck',
   args = { '--format', 'json1', '--external-sources' },
-  stdin = true,
   parse = require('guard.lint').from_json({
     get_diagnostics = function(...)
       return vim.json.decode(...).comments