Switch to kingpin flags (#639)

* Switch to kingpin flags

* Fix logrus vendoring

* Fix flags in main tests

* Fix vendoring versions

vendor/github.com/sirupsen/logrus/terminal_appengine.go

@@ -0,0 +1,10 @@
+// +build appengine
+
+package logrus
+
+import "io"
+
+// IsTerminal returns true if stderr's file descriptor is a terminal.
+func IsTerminal(f io.Writer) bool {
+	return true
+}