add vendor

vendor/github.com/mattn/go-isatty/isatty_windows.go

@@ -0,0 +1,19 @@
+// +build windows
+// +build !appengine
+
+package isatty
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+var kernel32 = syscall.NewLazyDLL("kernel32.dll")
+var procGetConsoleMode = kernel32.NewProc("GetConsoleMode")
+
+// IsTerminal return true if the file descriptor is terminal.
+func IsTerminal(fd uintptr) bool {
+	var st uint32
+	r, _, e := syscall.Syscall(procGetConsoleMode.Addr(), 2, fd, uintptr(unsafe.Pointer(&st)), 0)
+	return r != 0 && e == 0
+}