Merge pull request #82 from andrey-p/small-docs-fix

Small fix in ruler documentation example

lib/ruler.js

@@ -225,7 +225,7 @@ Ruler.prototype.after = function (afterName, ruleName, fn, options) {
  * ```javascript
  * var md = require('markdown-it')();
  *
- * md.core.ruler.push('emphasis', 'my_rule', function replace(state) {
+ * md.core.ruler.push('my_rule', function replace(state) {
  *   //...
  * });
  * ```