snowflake-client's `-url` option is intolerant of a missing path

I was following server-webrtc's README and I made a small mistake in the client torrc. Instead of

-url http://127.0.0.1:8080/

I had (no trailing slash):

-url http://127.0.0.1:8080

This caused the client to fail with this error:

2018/03/13 03:10:40 Negotiating via BrokerChannel...
Target URL:   
Front URL:   127.0.0.1:8080
2018/03/13 03:10:40 BrokerChannel Error: dial tcp: unknown port tcp/8080client
2018/03/13 03:10:40 Failed to retrieve answer. Retrying in 10 seconds

This is because the URL to request is built using string concatenation. It built the string "http://127.0.0.1:8080client" instead of "http://127.0.0.1:8080/client".

https://gitweb.torproject.org/pluggable-transports/snowflake.git/tree/client/rendezvous.go?id=ff8f3851082e8f7f8b4c8b99b161be35020aeb67#n83

request, err := http.NewRequest("POST", bc.url.String()+"client", data)