fix: add sticky article sort feature

Author: reco_luan

example/docs/views/category2/2016/121501.md

@@ -5,7 +5,7 @@ tags:
  - tag3
 categories: 
  - category2
-sticky: true
+sticky: 1
 ---
 
 first page in category2

example/docs/views/category2/2017/092101.md

@@ -7,6 +7,7 @@ categories:
  - category2
 keys:
  - '1232'
+sticky: 2
 ---
 
 second page in category2

mixins/index.js

@@ -18,8 +18,16 @@ export default {
           ? !(home == true || title == undefined || date === undefined || publish === false)
           : !(home == true || title == undefined || publish === false)
       })
+      this._sortstickyArr(stickyArr)
       return stickyArr.concat(posts)
     },
+    _sortstickyArr (posts) {
+      if (posts.length > 0) {
+        posts.sort((a, b) => {
+          return b.sticky - a.sticky
+        })
+      }
+    },
     _sortPostData (posts) {
       posts.sort((a, b) => {
         return this._getTimeNum(b) - this._getTimeNum(a)