update urfave/cli v1.22.1, go-md2man v2.0.0, blackfriday v2.0.1

This updates urfave/cli and its dependencies to v1.22.1:

- diff for urfave/cli: https://github.com/urfave/cli/compare/v1.22.0...v1.22.1
- diff for go-md2man: https://github.com/cpuguy83/go-md2man/compare/v1.0.10...v2.0.0
- diff for blackfriday: https://github.com/russross/blackfriday/compare/v1.5.2...v2.0.1

Also adds github.com/shurcooL/sanitized_anchor_name as a new dependency, which is
used by russross/blackfriday, but will be removed again in a future update (dependency
is already removed on the v2 branch through russross/blackfriday@919b1f5b9b

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/urfave/cli/context.go

@@ -313,9 +313,20 @@ func checkRequiredFlags(flags []Flag, context *Context) requiredFlagsErr {
 	var missingFlags []string
 	for _, f := range flags {
 		if rf, ok := f.(RequiredFlag); ok && rf.IsRequired() {
-			key := strings.Split(f.GetName(), ",")[0]
-			if !context.IsSet(key) {
-				missingFlags = append(missingFlags, key)
+			var flagPresent bool
+			var flagName string
+			for _, key := range strings.Split(f.GetName(), ",") {
+				if len(key) > 1 {
+					flagName = key
+				}
+
+				if context.IsSet(strings.TrimSpace(key)) {
+					flagPresent = true
+				}
+			}
+
+			if !flagPresent && flagName != "" {
+				missingFlags = append(missingFlags, flagName)
 			}
 		}
 	}