Update coverage to 4.2

[pyup-bot]

There's a new version of coverage available.
You are currently using 4.1. I have updated it to 4.2

Changelog

4.2

---

• Since concurrency=multiprocessing uses subprocesses, options specified on
  the coverage.py command line will not be communicated down to them. Only
  options in the configuration file will apply to the subprocesses.
  Previously, the options didn't apply to the subprocesses, but there was no
  indication. Now it is an error to use --concurrency=multiprocessing and
  other run-affecting options on the command line. This prevents
  failures like those reported in issue 495_.
• Filtering the HTML report is now faster, thanks to Ville Skyttä.

.. _issue 495: https://bitbucket.org/ned/coveragepy/issues/495/branch-and-concurrency-are-conflicting

4.2b1

---

Work from the PyCon 2016 Sprints!

• BACKWARD INCOMPATIBILITY: the coverage combine command now ignores an
  existing .coverage data file. It used to include that file in its
  combining. This caused confusing results, and extra tox "clean" steps. If
  you want the old behavior, use the new coverage combine --append option.
• The concurrency option can now take multiple values, to support programs
  using multiprocessing and another library such as eventlet. This is only
  possible in the configuration file, not from the command line. The
  configuration file is the only way for sub-processes to all run with the same
  options. Fixes issue 484_. Thanks to Josh Williams for prototyping.
• Using a concurrency setting of multiprocessing now implies
  --parallel so that the main program is measured similarly to the
  sub-processes.
• When using automatic subprocess measurement, running coverage commands
  would create spurious data files. This is now fixed, thanks to diagnosis and
  testing by Dan Riti. Closes issue 492.
• A new configuration option, report:sort, controls what column of the
  text report is used to sort the rows. Thanks to Dan Wandschneider, this
  closes issue 199_.
• The HTML report has a more-visible indicator for which column is being
  sorted. Closes issue 298_, thanks to Josh Williams.
• If the HTML report cannot find the source for a file, the message now
  suggests using the -i flag to allow the report to continue. Closes
  issue 231_, thanks, Nathan Land.
• When reports are ignoring errors, there's now a warning if a file cannot be
  parsed, rather than being silently ignored. Closes issue 396_. Thanks,
  Matthew Boehm.
• A new option for coverage debug is available: coverage debug config
  shows the current configuration. Closes issue 454_, thanks to Matthew
  Boehm.
• Running coverage as a module (python -m coverage) no longer shows the
  program name as __main__.py. Fixes issue 478_. Thanks, Scott Belden.
• The test_helpers module has been moved into a separate pip-installable
  package: unittest-mixins_.

.. _automatic subprocess measurement: http://coverage.readthedocs.io/en/latest/subprocess.html
.. _issue 199: https://bitbucket.org/ned/coveragepy/issues/199/add-a-way-to-sort-the-text-report
.. _issue 231: https://bitbucket.org/ned/coveragepy/issues/231/various-default-behavior-in-report-phase
.. _issue 298: https://bitbucket.org/ned/coveragepy/issues/298/show-in-html-report-that-the-columns-are
.. _issue 396: https://bitbucket.org/ned/coveragepy/issues/396/coverage-xml-shouldnt-bail-out-on-parse
.. _issue 454: https://bitbucket.org/ned/coveragepy/issues/454/coverage-debug-config-should-be
.. _issue 478: https://bitbucket.org/ned/coveragepy/issues/478/help-shows-silly-program-name-when-running
.. _issue 484: https://bitbucket.org/ned/coveragepy/issues/484/multiprocessing-greenlet-concurrency
.. _issue 492: https://bitbucket.org/ned/coveragepy/issues/492/subprocess-coverage-strange-detection-of
.. _unittest-mixins: https://pypi.python.org/pypi/unittest-mixins

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖