Update sphinx to 1.6.3

[pyup-bot]

There's a new version of Sphinx available.
You are currently using 1.6.2. I have updated it to 1.6.3

These links might come in handy: PyPI | Changelog | Homepage

Changelog

1.6.3

=====================================

Features added

• latex: hint that code-block continues on next page (refs: 3764, 3792)

Bugs fixed

• 3821: Failed to import sphinx.util.compat with docutils-0.14rc1
• 3829: sphinx-quickstart template is incomplete regarding use of alabaster
• 3772: 'str object' has no attribute 'filename'
• Emit wrong warnings if citation label includes hyphens (refs: 3565)
• 3858: Some warnings are not colored when using --color option
• 3775: Remove unwanted whitespace in default template
• 3835: sphinx.ext.imgmath fails to convert SVG images if project directory
  name contains spaces
• 3850: Fix color handling in make mode's help command
• 3865: use of self.env.warn in sphinx extension fails
• 3824: production lists apply smart quotes transform since Sphinx 1.6.1
• latex: fix \sphinxbfcode swallows initial space of argument
• 3878: Quotes in auto-documented class attributes should be straight quotes
  in PDF output
• 3881: LaTeX figure floated to next page sometimes leaves extra vertical
  whitespace
• 3885: duplicated footnotes raises IndexError
• 3873: Failure of deprecation warning mechanism of
  sphinx.util.compat.Directive
• 3874: Bogus warnings for "citation not referenced" for cross-file citations
• 3860: Don't download images when builders not supported images
• 3860: Remote image URIs without filename break builders not supported remote
  images
• 3833: command line messages are translated unintentionally with language
  setting.
• 3840: make checking epub_uid strict
• 3851, 3706: Fix about box drawing characters for PDF output
• 3900: autosummary could not find methods
• 3902: Emit error if latex_documents contains non-unicode string in py2

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

Happy merging! 🤖