Bump m2r from 0.2.1 to 0.3.1

Bumps m2r from 0.2.1 to 0.3.1.

Changelog

Sourced from m2r's changelog.

Version 0.3.0

• Drop support for Python 2.7, 3.4, 3.5, and 3.6
• Add compatibility with docutils 0.19
• Sync up assertion with changes in argparse
• Limit mistune dependency version range

Commits

• b49e336 Bump version: 0.3.0 → 0.3.1
• f23d003 Update README (Final Update)
• 5f951f3 Bump version: 0.2.1 → 0.3.0
• b64a06c Merge pull request #67 from claui/docutils-deprecation-fix
• de7be79 Limit mistune dependency version range
• 62143f2 Require Python 3.7+, add support for docutils 0.19
• 66f4a5a Separate flake8 check from test and update travis setting
• 77968c4 Fix test
• dfe57f9 Merge pull request #30 from morganwillcock/sphinx-codeblock
• 6b098e1 Merge pull request #38 from effigies/enh/sphinx2_parser
• Additional commits viewable in compare view