fix: add sourceType: 'unambiguous' to babel preset

[haoqunjiang]

Fixes #4773
The reasoning is stated at #4773 (comment)

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Underlying tools
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

Other information:

[viniciuskneves]

I was migrating to Vue CLI 4 manually and I think this option is not documented here: https://github.com/vuejs/vue-cli/tree/v4.2.3/packages/@vue/babel-preset-app

Am I looking at the right place or is it documented somewhere else?

[haoqunjiang]

It's a babel option: https://babeljs.io/docs/en/options#sourcetype

This PR only changes its default value to better handle edge cases. It doesn't affect actual usage.

[viniciuskneves]

It's a babel option: https://babeljs.io/docs/en/options#sourcetype

This PR only changes its default value to better handle edge cases. It doesn't affect actual usage.

Yep, but from @LinusBorg #4773 (comment) I thought it would be added to the docs (as a reference).

Just to be clear that it is not blocking me or anything. It is just because I was reading this PR + Issue mentioned and then doubled checked the docs.

I was using unambiguous in my project and could remove it after upgrading my dependencies as suggested.

[haoqunjiang]

Yeah, you are right, we do need to add it in the docs.

[haoqunjiang]

PR's welcome :)