nix: change default vm knot port to 6444

Signed-off-by: Seongmin Lee <[e-mail]>

docs/hacking.md

···
 # type `poweroff` at the shell to exit the VM
 ```
 
-This starts a knot on port 6000, a spindle on port 6555
+This starts a knot on port 6444, a spindle on port 6555
 with `ssh` exposed on port 2222.
 
 Once the services are running, head to

nix/vm.nix

···
             # knot
             {
               from = "host";
-              host.port = 6000;
-              guest.port = 6000;
+              host.port = 6444;
+              guest.port = 6444;
             }
             # spindle
             {
···
           motd = "Welcome to the development knot!\n";
           server = {
             owner = envVar "TANGLED_VM_KNOT_OWNER";
-            hostname = envVarOr "TANGLED_VM_KNOT_HOST" "localhost:6000";
+            hostname = envVarOr "TANGLED_VM_KNOT_HOST" "localhost:6444";
             plcUrl = plcUrl;
             jetstreamEndpoint = jetstream;
-            listenAddr = "0.0.0.0:6000";
+            listenAddr = "0.0.0.0:6444";
           };
         };
         services.tangled.spindle = {