Update proxy.auth.md

Adds comma to make the example a working example per the spec in TestParseKVSlice.go

Author: steffkelsey

docs/content/ref/proxy.auth.md

@@ -32,7 +32,7 @@ Supported htpasswd formats are detailed [here](https://github.com/tg123/go-htpas
     name=mybasicauth;type=basic;file=p/creds.htpasswd;refresh=30s
 
     # basic auth with multiple schemes
-    proxy.auth = name=mybasicauth;type=basic;file=p/creds.htpasswd;refresh=30s
+    proxy.auth = name=mybasicauth;type=basic;file=p/creds.htpasswd;refresh=30s,
                  name=myotherauth;type=basic;file=p/other-creds.htpasswd;realm=myrealm
 
 The default is