Bump xdoctest from 0.15.3 to 0.15.4 (#782)

Bumps [xdoctest](https://github.com/Erotemic/xdoctest) from 0.15.3 to 0.15.4.
- [Release notes](https://github.com/Erotemic/xdoctest/releases)
- [Changelog](https://github.com/Erotemic/xdoctest/blob/master/CHANGELOG.md)
- [Commits](Erotemic/xdoctest@0.15.3...0.15.4)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: cjolowicz

{{cookiecutter.project_name}}/poetry.lock

@@ -33,7 +33,7 @@ coverage = {extras = ["toml"], version = "^5.4"}
 safety = "^1.10.3"
 mypy = "^0.800"
 typeguard = "^2.10.0"
-xdoctest = {extras = ["colors"], version = "^0.15.3"}
+xdoctest = {extras = ["colors"], version = "^0.15.4"}
 sphinx = "^3.4.3"
 sphinx-autobuild = "^2020.9.1"
 pre-commit = "^2.10.1"