add vendor

vendor/github.com/mattn/go-isatty/README.md

@@ -0,0 +1,37 @@
+# go-isatty
+
+isatty for golang
+
+## Usage
+
+```go
+package main
+
+import (
+	"fmt"
+	"github.com/mattn/go-isatty"
+	"os"
+)
+
+func main() {
+	if isatty.IsTerminal(os.Stdout.Fd()) {
+		fmt.Println("Is Terminal")
+	} else {
+		fmt.Println("Is Not Terminal")
+	}
+}
+```
+
+## Installation
+
+```
+$ go get github.com/mattn/go-isatty
+```
+
+# License
+
+MIT
+
+# Author
+
+Yasuhiro Matsumoto (a.k.a mattn)