chore(package): update vue-docgen-api to version 4.22.1

Closes #18

Author: greenkeeper[bot]

package.json

@@ -160,7 +160,7 @@
     "url-loader": "^3.0.0",
     "vue": "^2.5.22",
     "vue-directive-tooltip": "~1.6.3",
-    "vue-docgen-api": "^3.19.5",
+    "vue-docgen-api": "^4.22.1",
     "vue-jest": "^3.0.4",
     "vue-loader": "^15.7.1",
     "vue-style-loader": "^4.1.2",