Update sphinx-autodoc-typehints from 1.7.0 to 1.8.0

Author: pyup-bot

dev-requirements.txt

@@ -21,7 +21,7 @@ pytest-cov==2.7.1  # Measure code coverage
 pytest==5.1.2  # Test runners
 PyYAML==5.1.2
 Sphinx==2.2.0
-sphinx-autodoc-typehints==1.7.0
+sphinx-autodoc-typehints==1.8.0
 sphinxcontrib-spelling==4.3.0
 twine==1.13.0
 versioneer==0.18