feat(waitFor): improve error message for non-function callbacks

[Belco90]

What:
Closes #509

Why:
To improve error message and error stack trace

How:
Checking if callback is a function.

Checklist:

• Documentation added to the
  docs site
• I've prepared a PR for types targeting
  DefinitelyTyped
• Tests
• Ready to be merged
  

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[codecov]

Codecov Report

Merging #515 into master will not change coverage by %.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #515   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           23        23           
  Lines          426       428    +2     
  Branches       101       102    +1     
=========================================
+ Hits           426       428    +2     

Impacted Files	Coverage Δ
src/wait-for.js	100.00% <100.00%> (ø)

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[eps1lon]

Looks good. Just some minor nitpicks.

[eps1lon]

@Belco90 Looking good, thanks!

[kentcdodds]

🎉 This PR is included in version 7.2.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀