Fixed a little error (#379)

NefixEstrada · QingWei-Li · commit 1c5d59422873 · 2018-02-05T09:37:10.000+08:00
There's nothing fancy on this commit
diff --git a/docs/helpers.md b/docs/helpers.md
@@ -78,7 +78,7 @@ You will get `<a href="/demo/">link</a>`html. Do not worry, you can still set ti
 * [ ] foo
  * bar
  * [x] baz
- * [] bam
+ * [ ] bam
    * [ ] bim
    * [ ] lim
 
