[server/log] Use millisecond precision in realtive time mode

We don't get more precise timings that anyway unless we were to use the 
performance timers

server/Helpers/Log.mjs

@@ -21,7 +21,7 @@ class Log {
 		}
 		let prefix = (new Date()).toISOString();
 		if(this.settings.logging.date_display_mode == "relative") {
-			prefix = ((new Date() - this.start_time) / 1000).toFixed(4);
+			prefix = ((new Date() - this.start_time) / 1000).toFixed(3);
 		}
 		
 		func(`${this.a.locol}[${prefix}]${this.a.reset}`, ...items);