Add shouldExtractValueFromUnion and fix default value bug

[DSil]

This PR includes two commits:

• one bumps the react-docgen-typescript dependency to the latest version
• the second:
  • Adds support for shouldExtractValueFromUnion parser option Note 1
  • Fixes a bug with non-string default values Note 2

Screenshots

Before:  Now: 

Note 1:

shouldExtractValueFromUnion allows a more complete parsing than shouldExtractLiteralValuesFromEnum. It supports union types with multiple types (not only strings). I believe the latter is no longer needed, since the first covers the same scenarios, but I prefer to avoid a breaking change and keep supporting both, since react-docgen-typescript also supports both.

Note 2:

When using a default value that is not a string, the babel parser simply could not compile, as it was always expecting a string as default value. This is now fixed by transforming the value into a string. (See Problem with tests)

Problem with tests:

Running the tests locally was not a problem (using node 12). However, the pre-commit also runs the tests and it constantly failed because of a known bug with node and the toString method (implicitly called in the template string transformation). I was not able to enforce this to run on node 11.12.0 or above (the version that fixes this issue). Are you able to add this? Or is this not an issue, since the tests run locally with no problem?

Changelog and README:

I updated them as I thought it should be but you're free to update them as it best suits you.

Thanks.

[DSil]

Hi @strothj are you still maintaining this project?

[strothj]

Unfortunately I’ve had no time as I’ve been stuck in a mix of travel and work. I don’t use this project myself personally. I can pass the reigns to you if you’re interested.

[DSil]

I would really appreciate if I could just use this with these features, so that I don’t need to build something similar on my side. I guess I can take the reigns if you’re open to it. There doesn’t seem to be much going around anyway :)

[strothj]

@DSil I've invited you as a collaborator to this repository. I couldn't transfer you the repository yet because you have an existing fork on your account. I'm guessing the pull requests will need to be taken care of first. What is your NPM username?

[DSil]

I do not have an NPM account. I’ll take a moment to do that later today

[DSil]

My npm username is the same as github: dsil

[strothj]

I invited you in npm. You should now be able to handle the repo and npm package.

[DSil]

Thank you @strothj, I'll handle it.