Fix default receive.timeout

This should be in milliseconds, not seconds. Set the default to be
2 minutes in milliseconds and update the documentation to reflect
that milliseconds are the default unit of time used here.

Change-Id: I50d74e91f4acec2b91daf59a16966cb89045d064

gerrit-server/src/main/java/com/google/gerrit/server/git/AsyncReceiveCommits.java

@@ -73,8 +73,8 @@ public class AsyncReceiveCommits implements PreReceiveHook {
     long getTimeoutMillis(@GerritServerConfig final Config cfg) {
       return ConfigUtil.getTimeUnit(
           cfg, "receive", null, "timeout",
-          TimeUnit.SECONDS.convert(2, TimeUnit.MINUTES),
-          TimeUnit.SECONDS);
+          TimeUnit.MINUTES.toMillis(2),
+          TimeUnit.MILLISECONDS);
     }
   }