chore(vue-test-utils) bump version to fix scopedSlots trim bug

From vuejs/vue-test-utils#706

Author: darrenjennings

package.json

@@ -8,7 +8,7 @@
   "repository": "git@github.com:Kong/kongponents.git",
   "private": true,
   "bin": {
-    "kpm": "./cli/index.js" 
+    "kpm": "./cli/index.js"
   },
   "workspaces": [
     "packages/*"
@@ -31,7 +31,7 @@
     "@storybook/addon-links": "3.4.10",
     "@storybook/addon-notes": "3.4.10",
     "@storybook/vue": "3.4.10",
-    "@vue/test-utils": "1.0.0-beta.20",
+    "@vue/test-utils": "1.0.0-beta.28",
     "babel-core": "6.26.3",
     "babel-jest": "^23.6.0",
     "babel-loader": "7.1.4",