Merge v1.2.1-master

Signed-off-by: Emile Vauge <emile@vauge.com>

vendor/github.com/Sirupsen/logrus/terminal_notwindows.go

@@ -4,18 +4,25 @@
 // license that can be found in the LICENSE file.
 
 // +build linux darwin freebsd openbsd netbsd dragonfly
+// +build !appengine
 
 package logrus
 
 import (
+	"io"
+	"os"
 	"syscall"
 	"unsafe"
 )
 
 // IsTerminal returns true if stderr's file descriptor is a terminal.
-func IsTerminal() bool {
-	fd := syscall.Stderr
+func IsTerminal(f io.Writer) bool {
 	var termios Termios
-	_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), ioctlReadTermios, uintptr(unsafe.Pointer(&termios)), 0, 0, 0)
-	return err == 0
+	switch v := f.(type) {
+	case *os.File:
+		_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(v.Fd()), ioctlReadTermios, uintptr(unsafe.Pointer(&termios)), 0, 0, 0)
+		return err == 0
+	default:
+		return false
+	}
 }