Fix comment stating default http2 behavior in options

Author: mark200

options.go

@@ -97,7 +97,7 @@ type TransportOptions struct {
 	ForceJaegerSample   bool              `long:"force-jaeger-sample" description:"Force all requests to be sampled for Jaeger tracing (use with --jaeger)"`
 
 	// HTTP/2 specific options
-	UseHTTP2 bool `long:"http2" description:"Enable HTTP/2 for HTTP transport (enabled by default)"`
+	UseHTTP2 bool `long:"http2" description:"Enable HTTP/2 for HTTP transport"`
 
 	// This is a hack to work around go-flags not allowing disabling flags:
 	// https://github.com/jessevdk/go-flags/issues/191