Change ValueError to io.UnsupportedOperation in capture.py. Resolves …

[metasyn]

…issue #2276

Thanks for submitting a PR, your contribution is really appreciated!

Here's a quick checklist that should be present in PRs:

• Target: for bug or doc fixes, target master; for new features, target features;

Unless your change is trivial documentation fix (e.g., a typo or reword of a small section) please:

• Make sure to include one or more tests for your change;
• Add yourself to AUTHORS;
• Add a new entry to CHANGELOG.rst

For such a simple change, I only modified an existing test.

[coveralls]

Coverage increased (+0.0008%) to 92.711% when pulling 6c393d0 on metasyn:DontReadFromInput-exceptions into 5e52a4d on pytest-dev:master.

[nicoddemus]

Looks great, many thanks!

I took the liberty of rebasing your commits on the new master and tweaking the CHANGLOG a bit in #2313, so I'm closing this in favor of the new PR. Thanks again!