chore: replace expect-legacy package with chai

[bdkopen]

Replaces expect-legacy with chai.

expect-legacy is an unmaintained fork of expect. It appears to be a fork because expect joined the jest project. Given that the fork hasn't been updated in 8 years and has 99 sub-dependencies, it's a good time to migrate.

chai is good fit because it's often used with mocha already and is a recommended package on the mocha docs. It keeps this update simple because moving everything to jest would include migrating away from mocha. Since mocha and chai are both well maintained, this doesn't seem necessary at this point.

The toExist function in expect is just checking for a truthy value, so to.be.ok is the equivalent in chai. Similarly, toBe is replaced with to.equal.

Please let me know if any changes are necessary. Thanks!

[jeffbski]

@bdkopen Thanks for doing this upgrade to a better package.

[jeffbski]

Published in https://github.com/jeffbski/wait-on/releases/tag/v9.0.2