Rename shallow to shallowMount

As discussed with @eddyerburgh, I’ve had to explain to a lot of people that shallow does actually mount, it’s just a shallow mount. 😄 This rename would make that clearer.

[lmiller1990]

Another potentially less confusing alternative could be a shallow option:

const wrapper = mount(Component, {
  shallow: true
})

Although I don’t have a strong opinion either way.

[FernandoBasso]

Since VTU is about unit testing, and that more or less means one does not mount/test child components, what about mount defaulting to “shallow” and then allowing the user set it to true when they need, like @lmiller1990’s approach?

I understand that perhaps people would complain “hey, my components do not get properly mounted” if they don’t see child components mounted as well and didn’t read the docs about shallow/non-shallow.

Anyway, that is another idea that may or may not work.