Fix missing vendor packages

The switch to urfave/cli had a use of a /v2 API, which
go modules handles correctly but vndr ignores. Downgrade
urfave/cli for now until the switch to go modules. Add
missing dependencies, which vndr now sees.
Note that CI was not catching this issue, it seems that
some part of the build process was pulling in dependencies
even if they weren't in vendor, causing the build to work.
However the vendor check was not seeing it. The ARM build
didn't pull in other dependencies into the gopath, causing
those builds to break.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

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

@@ -8,7 +8,7 @@ import (
 	"strings"
 	"text/template"
 
-	"github.com/cpuguy83/go-md2man/v2/md2man"
+	"github.com/cpuguy83/go-md2man/md2man"
 )
 
 // ToMarkdown creates a markdown string for the `*App`
@@ -57,9 +57,6 @@ func prepareCommands(commands []Command, level int) []string {
 	coms := []string{}
 	for i := range commands {
 		command := &commands[i]
-		if command.Hidden {
-			continue
-		}
 		usage := ""
 		if command.Usage != "" {
 			usage = command.Usage