Update pyproject.toml

Fix invalid sphinx spec

Author: deto

pyproject.toml

@@ -55,7 +55,7 @@ scanpy = {version = "*", optional = true}
 
 [tool.poetry.extras]
 test = ["pytest", "scanpy"]
-docs=["sphinx-book-theme", "nbsphinx", "sphinx>", "ipython"]
+docs=["sphinx-book-theme", "nbsphinx", "sphinx", "ipython"]
 
 [tool.poetry.dev-dependencies]
 
@@ -65,4 +65,4 @@ build-backend = "poetry.masonry.api"
 requires = [
   "poetry>=1.0",
   "setuptools", # keep it here or "pip install -e" would fail
-]
+]