Upgrade urfave/cli to v2 (#614)

* Upgrade cli to v2
* Re-vendor

vendor/github.com/urfave/cli/v2/flag_bool.go

@@ -0,0 +1,106 @@
+package cli
+
+import (
+	"flag"
+	"fmt"
+	"strconv"
+)
+
+// BoolFlag is a flag with type bool
+type BoolFlag struct {
+	Name        string
+	Aliases     []string
+	Usage       string
+	EnvVars     []string
+	FilePath    string
+	Required    bool
+	Hidden      bool
+	Value       bool
+	DefaultText string
+	Destination *bool
+	HasBeenSet  bool
+}
+
+// IsSet returns whether or not the flag has been set through env or file
+func (f *BoolFlag) IsSet() bool {
+	return f.HasBeenSet
+}
+
+// String returns a readable representation of this value
+// (for usage defaults)
+func (f *BoolFlag) String() string {
+	return FlagStringer(f)
+}
+
+// Names returns the names of the flag
+func (f *BoolFlag) Names() []string {
+	return flagNames(f)
+}
+
+// IsRequired returns whether or not the flag is required
+func (f *BoolFlag) IsRequired() bool {
+	return f.Required
+}
+
+// TakesValue returns true of the flag takes a value, otherwise false
+func (f *BoolFlag) TakesValue() bool {
+	return false
+}
+
+// GetUsage returns the usage string for the flag
+func (f *BoolFlag) 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 *BoolFlag) GetValue() string {
+	return ""
+}
+
+// Apply populates the flag given the flag set and environment
+func (f *BoolFlag) Apply(set *flag.FlagSet) error {
+	if val, ok := flagFromEnvOrFile(f.EnvVars, f.FilePath); ok {
+		if val != "" {
+			valBool, err := strconv.ParseBool(val)
+
+			if err != nil {
+				return fmt.Errorf("could not parse %q as bool value for flag %s: %s", val, f.Name, err)
+			}
+
+			f.Value = valBool
+			f.HasBeenSet = true
+		}
+	}
+
+	for _, name := range f.Names() {
+		if f.Destination != nil {
+			set.BoolVar(f.Destination, name, f.Value, f.Usage)
+			continue
+		}
+		set.Bool(name, f.Value, f.Usage)
+	}
+
+	return nil
+}
+
+// Bool looks up the value of a local BoolFlag, returns
+// false if not found
+func (c *Context) Bool(name string) bool {
+	if fs := lookupFlagSet(name, c); fs != nil {
+		return lookupBool(name, fs)
+	}
+	return false
+}
+
+func lookupBool(name string, set *flag.FlagSet) bool {
+	f := set.Lookup(name)
+	if f != nil {
+		parsed, err := strconv.ParseBool(f.Value.String())
+		if err != nil {
+			return false
+		}
+		return parsed
+	}
+	return false
+}