[2336] Fix API for DotCover.report

[TomasMorton]

Description

As per #2336, fixes the definition of the DotCover.report function, as it was not handling the failBuild param of buildParamsAndExecute, added in #990.

Note that this would be a "breaking change" for anyone already using the module, because they will be passing in the parameter themselves.

TODO

• unit or integration test exists (or short reasoning why it doesn't make sense)

  Note: Consider using the CreateProcess API which can be tested more easily, see https://github.com/fsharp/FAKE/pull/2131/files#diff-4fb4a77e110fbbe8210205dfe022389b for an example (the changes in the DotNet.Testing.NUnit module)

• boy scout rule: "leave the code behind in a better state than you found it" (fix warnings, obsolete members or code-style in the places you worked in)

• Fake 5 API guideline is honored

[matthid]

Nice catch!
While technically a breaking change, we will revert this (just as you suggest in this PR) as I indeed consider this a bugfix.
Please also feel free to use failbuild=true. We can always set to false later, but if we already break we can fix that default as well (maybe even for the DotCoverMerge function?). This was basically the pre 2015 behavior...

[TomasMorton]

Hey @matthid,

Really sorry, I've been too busy to get around to making modifications. I agree it would have made more sense to have fail as true.

Thank you for merging the fix.