chore: switch license from Apache to MIT

[rwalle61]

This is a one-time switch to MIT license, for the reasons below:

Motivations:

• We are a Jest plugin and Chai plugin, so it makes sense for us to match the license of Jest and Chai, which is MIT.
• This won't make much/any practical difference, as Apache and MIT are basically equally permissive.
• MIT is much shorter to read, so easier to understand
• MIT is a bit more popular in general and I think much more popular in the Jest / Chai / general JS testing space

Risks:

• As I understand things, Apache is basically like MIT but (A) anyone who modifies this code will have to specify their modifications explicitly and (B) anyone wanting to patent something using this code will have explict permission to do so, whereas with the MIT license this is only heavily implied
• Current users may not be happy with this switch (for the above reason or another I'm not aware of) and therefore stop using this package.

Sources:

• https://resources.whitesourcesoftware.com/blog-whitesource/top-10-apache-license-questions-answered
• https://www.quora.com/Whats-the-difference-between-Apache-v2-0-and-MIT-license-What-are-the-major-consequences-of-using-Apache-software-over-MIT
• https://snyk.io/blog/mit-apache-bsd-fairest-of-them-all/
• google this

Decision:

• Leave this PR open for at least 1 week - if anyone objects to the license change, please downvote this and leave a comment explaining why
• If there are no significant objections, publish this under a new minor version (we don't do major versions yet) to signify a change to users

[codecov]

Codecov Report

Merging #211 (35b8bca) into master (6bc5ccb) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #211   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           33        33           
  Lines          670       670           
  Branches        49        49           
=========================================
  Hits           670       670           

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