go.mod: update gitlab dep to v0.30.1

Releases after github.com/xanzy/go-gitlab@v0.31.0 introduce breaking
changes to the NewClient call.

Addresses #94

vendor/github.com/cpuguy83/go-md2man/v2/md2man/md2man.go

@@ -0,0 +1,14 @@
+package md2man
+
+import (
+	"github.com/russross/blackfriday/v2"
+)
+
+// Render converts a markdown document into a roff formatted document.
+func Render(doc []byte) []byte {
+	renderer := NewRoffRenderer()
+
+	return blackfriday.Run(doc,
+		[]blackfriday.Option{blackfriday.WithRenderer(renderer),
+			blackfriday.WithExtensions(renderer.GetExtensions())}...)
+}