Update coconut requirement from <2.3.0,>=1.4.3 to >=1.4.3,<3.1.0 (#517)

Updates the requirements on [coconut](https://github.com/evhub/coconut) to permit the latest version.
- [Release notes](https://github.com/evhub/coconut/releases)
- [Commits](evhub/coconut@v1.4.3...v3.0.0)

---
updated-dependencies:
- dependency-name: coconut
  dependency-type: direct:production
...

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

Author: dependabot[bot]

pyproject.toml

@@ -71,7 +71,7 @@ rtd = [
     "alabaster",
     "altair",
     "bokeh",
-    "coconut>=1.4.3,<2.3.0",
+    "coconut>=1.4.3,<3.1.0",
     "ipykernel~=5.5",
     "ipywidgets",
     "jupytext>=1.11.2,<1.15.0",