Update mkdocs-material from 8.1.2 to 8.1.3 (#180)

requirements.dev.txt

@@ -10,7 +10,7 @@ bumpversion==0.6.0
 codecov==2.1.12
 pytest-cov==3.0.0
 mkdocs == 1.2.3
-mkdocs-material==8.1.2
+mkdocs-material==8.1.3
 mkdocs-markdownextradata-plugin==0.2.5
 mkdocs-mermaid2-plugin==0.5.2
 markdown-include==0.6.0