Add vue-fixed-header via yarn

Author: n-makarin

package.json

@@ -10,6 +10,7 @@
   "dependencies": {
     "core-js": "^3.4.4",
     "vue": "^2.6.10",
+    "vue-fixed-header": "^3.2.14",
     "vue-router": "^3.1.3",
     "vue2-smooth-scroll": "^1.2.0",
     "vuex": "^3.1.2"