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/flag_string.go

@@ -1,98 +0,0 @@
-package cli
-
-import "flag"
-
-// StringFlag is a flag with type string
-type StringFlag struct {
-	Name        string
-	Usage       string
-	EnvVar      string
-	FilePath    string
-	Required    bool
-	Hidden      bool
-	TakesFile   bool
-	Value       string
-	Destination *string
-}
-
-// String returns a readable representation of this value
-// (for usage defaults)
-func (f StringFlag) String() string {
-	return FlagStringer(f)
-}
-
-// GetName returns the name of the flag
-func (f StringFlag) GetName() string {
-	return f.Name
-}
-
-// IsRequired returns whether or not the flag is required
-func (f StringFlag) IsRequired() bool {
-	return f.Required
-}
-
-// TakesValue returns true of the flag takes a value, otherwise false
-func (f StringFlag) TakesValue() bool {
-	return true
-}
-
-// GetUsage returns the usage string for the flag
-func (f StringFlag) GetUsage() string {
-	return f.Usage
-}
-
-// GetValue returns the flags value as string representation and an empty
-// string if the flag takes no value at all.
-func (f StringFlag) GetValue() string {
-	return f.Value
-}
-
-// Apply populates the flag given the flag set and environment
-// Ignores errors
-func (f StringFlag) Apply(set *flag.FlagSet) {
-	_ = f.ApplyWithError(set)
-}
-
-// ApplyWithError populates the flag given the flag set and environment
-func (f StringFlag) ApplyWithError(set *flag.FlagSet) error {
-	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
-		f.Value = envVal
-	}
-
-	eachName(f.Name, func(name string) {
-		if f.Destination != nil {
-			set.StringVar(f.Destination, name, f.Value, f.Usage)
-			return
-		}
-		set.String(name, f.Value, f.Usage)
-	})
-
-	return nil
-}
-
-// String looks up the value of a local StringFlag, returns
-// "" if not found
-func (c *Context) String(name string) string {
-	return lookupString(name, c.flagSet)
-}
-
-// GlobalString looks up the value of a global StringFlag, returns
-// "" if not found
-func (c *Context) GlobalString(name string) string {
-	if fs := lookupGlobalFlagSet(name, c); fs != nil {
-		return lookupString(name, fs)
-	}
-	return ""
-}
-
-func lookupString(name string, set *flag.FlagSet) string {
-	f := set.Lookup(name)
-	if f != nil {
-		parsed, err := f.Value.String(), error(nil)
-		if err != nil {
-			return ""
-		}
-		return parsed
-	}
-	return ""
-}