Bump required Hugo version to v0.21

theme.toml

@@ -4,7 +4,7 @@ licenselink = "https://github.com/spf13/hyde/blob/master/LICENSE.md"
 description = "An elegant open source and mobile first theme"
 tags = ["blog", "company"]
 features = ["blog", "themes", "disqus"]
-min_version = 0.20
+min_version = 0.21
 
 [author]
     name = "spf13"