fix: Cannot find module 'rc' error when use npx (#210)

markdownlint.js

@@ -10,7 +10,7 @@ const options = program.opts();
 const differenceWith = require('lodash.differencewith');
 const flatten = require('lodash.flatten');
 const markdownlint = require('markdownlint');
-const rc = require('rc');
+const rc = require('run-con');
 const glob = require('glob');
 const minimatch = require('minimatch');
 const minimist = require('minimist');