Implement isatty() to make the CaptureOutput compatible with Django requirements

[carlio]

Description

When using prospector (with pylint) on a Django project, Django runs into a problem testing whether the sysout/stderr is a TTY, but prospector wraps that in CaptureOutput.

Please ignore that I can't spell "bugfix" in the branch name 🙄

Related Issue

Fixes #703

Motivation and Context

This PR implements that particular test for the case of prospector+Django

How Has This Been Tested?

I had this problem on my own local project, and this code fixed it - it was a simple missing implementation on the wrapper class.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• My change requires a change to the dependencies
• I have updated the dependencies accordingly
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[Pierre-Sassoulas]

Wouldn't have noticed the spelling in the branch name.. if you didn't point it out 😄