vendor: update all dependencies except Azure SDK

The Azure SDK doesn't support Go 1.5 anymore. We can't upgrade it until
Go 1.8 comes out.

vendor/github.com/nsf/termbox-go/README.md

@@ -24,6 +24,7 @@ There are also some interesting projects using termbox-go:
  - [snake-game](https://github.com/DyegoCosta/snake-game) is an implementation of the Snake game.
  - [gone](https://github.com/guillaumebreton/gone) is a CLI pomodoro® timer.
  - [Spoof.go](https://github.com/sabey/spoofgo) controllable movement spoofing from the cli
+ - [lf](https://github.com/gokcehan/lf) is a terminal file manager
 
 ### API reference
 [godoc.org/github.com/nsf/termbox-go](http://godoc.org/github.com/nsf/termbox-go)

vendor/github.com/nsf/termbox-go/api.go

@@ -343,7 +343,6 @@ func PollEvent() Event {
 			return event
 		}
 	}
-	panic("unreachable")
 }
 
 // Returns the size of the internal back buffer (which is mostly the same as

vendor/github.com/nsf/termbox-go/termbox.go

@@ -233,10 +233,7 @@ func send_char(x, y int, ch rune) {
 func flush() error {
 	_, err := io.Copy(out, &outbuf)
 	outbuf.Reset()
-	if err != nil {
-		return err
-	}
-	return nil
+	return err
 }
 
 func send_clear() error {