const golang.org/x/net/http2.defaultUserAgent

2 uses

	golang.org/x/net/http2 (current package)
		transport.go#L50: 	defaultUserAgent = "Go-http-client/2.0"
		transport.go#L1964: 			f("user-agent", defaultUserAgent)

The pages are generated with Golds v0.4.9. (GOOS=linux GOARCH=amd64)