tag error is wrong when return error

[salmon7]

error tag is always is false in span, even return error in handler.

the code is here:
https://github.com/opentracing-contrib/echo/blob/master/middleware.go#L58~L63

			if err := next(c); err != nil {
				sp.SetTag("error", true)
				c.Error(err)
			}

			sp.SetTag("error", false)

Maybe it should be changed to:

			err = next(c)
			if err != nil {
				sp.SetTag("error", true)
				c.Error(err)
			} else {
				sp.SetTag("error", false)
			}

[fananchong]

I also found this problem