fix: don't use configured proxy for unix socket (#7)

* fix: don't use configured proxy for unix socket

* Update register.go

Co-authored-by: Peter Bourgon <peterbourgon@users.noreply.github.com>

* Update register.go

Co-authored-by: Peter Bourgon <peterbourgon@users.noreply.github.com>

---------

Co-authored-by: Peter Bourgon <peterbourgon@users.noreply.github.com>

register.go

@@ -20,12 +20,13 @@ import (
 // so uses the same configuration: timeouts, TLS settings, and so on. Connection
 // pooling should also work as normal. One caveat: only the DialContext and
 // DialTLSContext dialers are respected; the Dial and DialTLS dialers are
-// explicitly removed and ignored.
+// explicitly removed and ignored. Any configured Proxy is also discarded.
 func Register(t *http.Transport) {
 	copy := t.Clone()
 
 	copy.Dial = nil    //lint:ignore SA1019 yes, it's deprecated, that's the point
 	copy.DialTLS = nil //lint:ignore SA1019 yes, it's deprecated, that's the point
+	copy.Proxy = nil   // Proxy doesn't support Unix sockets, so drop it
 
 	switch {
 	case copy.DialContext == nil && copy.DialTLSContext == nil: