chore(deps): update twine requirement from ~=1.14 to ~=1.15

Updates the requirements on [twine](https://github.com/pypa/twine) to permit the latest version.
- [Release notes](https://github.com/pypa/twine/releases)
- [Changelog](https://github.com/pypa/twine/blob/master/docs/changelog.rst)
- [Commits](pypa/twine@1.14.0...1.15.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -9,4 +9,4 @@ Sphinx~=2.2
 sphinxcontrib-log-cabinet~=1.0
 sphinxcontrib-websupport~=1.1
 pip~=19.2
-twine~=1.14
+twine~=1.15