Enables child component stubs

[tim-maguire]

Hello Daniel.

This PR enables the vue-test-utils stubs options.

Example use case

This:

import { FontAwesomeIcon } from "@fortawesome/vue-fontawesome"
import { library, config } from "@fortawesome/fontawesome-svg-core"
import { faSearch } from "@fortawesome/free-solid-svg-icons"
import { render, cleanup } from "../../src"
import Form from "./components/Form"

afterEach(cleanup)

library.add(faSearch)

test("Form contians with search button", () => {
  const { getByText } = render(Form, {}, vue => {
    vue.component(FontAwesomeIcon.name, FontAwesomeIcon)
  })
  getByText("Search now")
})

Can reduce to:

import { render, cleanup } from "../../src"
import Form from "./components/Form"

afterEach(cleanup)

test("Form contians with search button", () => {
  const { getByText } = render(Form, {
    stubs: ['font-awesome-icon']
  })
  getByText("Search now")
})

[coveralls]

Pull Request Test Coverage Report for Build 72

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.08%) to 95.082%

---

Totals
Change from base Build 70:	0.08%
Covered Lines:	41
Relevant Lines:	42

---

💛 - Coveralls

[dfcook]

I like this but wonder can it be taken further, should we use rest params to allow the full range of options to be passed to mount?

I've created an alternative PR, #12 . Do you want to take a look and give me your thoughts?