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_slice.go

@@ -1,138 +0,0 @@
-package cli
-
-import (
-	"flag"
-	"fmt"
-	"strings"
-)
-
-// StringSlice is an opaque type for []string to satisfy flag.Value and flag.Getter
-type StringSlice []string
-
-// Set appends the string value to the list of values
-func (f *StringSlice) Set(value string) error {
-	*f = append(*f, value)
-	return nil
-}
-
-// String returns a readable representation of this value (for usage defaults)
-func (f *StringSlice) String() string {
-	return fmt.Sprintf("%s", *f)
-}
-
-// Value returns the slice of strings set by this flag
-func (f *StringSlice) Value() []string {
-	return *f
-}
-
-// Get returns the slice of strings set by this flag
-func (f *StringSlice) Get() interface{} {
-	return *f
-}
-
-// StringSliceFlag is a flag with type *StringSlice
-type StringSliceFlag struct {
-	Name      string
-	Usage     string
-	EnvVar    string
-	FilePath  string
-	Required  bool
-	Hidden    bool
-	TakesFile bool
-	Value     *StringSlice
-}
-
-// String returns a readable representation of this value
-// (for usage defaults)
-func (f StringSliceFlag) String() string {
-	return FlagStringer(f)
-}
-
-// GetName returns the name of the flag
-func (f StringSliceFlag) GetName() string {
-	return f.Name
-}
-
-// IsRequired returns whether or not the flag is required
-func (f StringSliceFlag) IsRequired() bool {
-	return f.Required
-}
-
-// TakesValue returns true of the flag takes a value, otherwise false
-func (f StringSliceFlag) TakesValue() bool {
-	return true
-}
-
-// GetUsage returns the usage string for the flag
-func (f StringSliceFlag) 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 StringSliceFlag) GetValue() string {
-	if f.Value != nil {
-		return f.Value.String()
-	}
-	return ""
-}
-
-// Apply populates the flag given the flag set and environment
-// Ignores errors
-func (f StringSliceFlag) Apply(set *flag.FlagSet) {
-	_ = f.ApplyWithError(set)
-}
-
-// ApplyWithError populates the flag given the flag set and environment
-func (f StringSliceFlag) ApplyWithError(set *flag.FlagSet) error {
-	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
-		newVal := &StringSlice{}
-		for _, s := range strings.Split(envVal, ",") {
-			s = strings.TrimSpace(s)
-			if err := newVal.Set(s); err != nil {
-				return fmt.Errorf("could not parse %s as string value for flag %s: %s", envVal, f.Name, err)
-			}
-		}
-		if f.Value == nil {
-			f.Value = newVal
-		} else {
-			*f.Value = *newVal
-		}
-	}
-
-	eachName(f.Name, func(name string) {
-		if f.Value == nil {
-			f.Value = &StringSlice{}
-		}
-		set.Var(f.Value, name, f.Usage)
-	})
-
-	return nil
-}
-
-// StringSlice looks up the value of a local StringSliceFlag, returns
-// nil if not found
-func (c *Context) StringSlice(name string) []string {
-	return lookupStringSlice(name, c.flagSet)
-}
-
-// GlobalStringSlice looks up the value of a global StringSliceFlag, returns
-// nil if not found
-func (c *Context) GlobalStringSlice(name string) []string {
-	if fs := lookupGlobalFlagSet(name, c); fs != nil {
-		return lookupStringSlice(name, fs)
-	}
-	return nil
-}
-
-func lookupStringSlice(name string, set *flag.FlagSet) []string {
-	f := set.Lookup(name)
-	if f != nil {
-		parsed, err := (f.Value.(*StringSlice)).Value(), error(nil)
-		if err != nil {
-			return nil
-		}
-		return parsed
-	}
-	return nil
-}