startsWith instead of indexOf

[Connormiha]

What:
Just simplified checking for error name

Why:

How:
indexOf -> startsWith

Checklist:

• Documentation added to the
  docs site
• Tests
• Typescript definitions updated
• Ready to be merged
  

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[codecov]

Codecov Report

Merging #552 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #552   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           3      3           
  Lines          95     95           
  Branches       15     15           
=====================================
  Hits           95     95

Impacted Files	Coverage Δ
src/act-compat.js	100% <ø> (ø)	⬆️

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[eps1lon]

Thank you for working on this. Could you explain what the purpose of this PR is?

startsWith is not supported in IE11 and babel can't transpile these to use core-js as far as I know. In the current state we can't accept this PR.

[Connormiha]

@eps1lon if IE11 supported, you right. This PR will break IE11.

[eps1lon]

@eps1lon if IE11 supported, you right.

I don't think we officially support it as in "if it doesn't work in IE 11 we won't prioritize it i.e. PRs welcome". At least I'm using it in IE 11 and am therefore interested in it working as good as possible.