📝 Fix version reference

Author: thinkyhead

docs/Serial.md

@@ -5,7 +5,7 @@ While many provide a Arduino-like Serial class, it's not all of them, and the di
 
 Moreover, many platform have intrinsic needs about serial port (like forwarding the output on multiple serial port, providing a *serial-like* telnet server, mixing USB-based serial port with SD card emulation) that are difficult to handle cleanly in the other platform serial logic.
 
-Starting with version `2.0.9`, Marlin provides a common interface for its serial needs.
+Starting with version 2.0.8, Marlin provides a common interface for its serial needs.
 
 ## Common interface