Add suitable enviornment for rule

xinput needs DISPLAY and XAUTHORITY variables set to work.

src/rules/90-hid-mouse.rules

@@ -3,7 +3,9 @@
 # insertion, removal. Actually, usb events are triggered when usb and
 # usb interface are binding but hid is more specific and happen once for each
 # action. change action is not used because 
-SUBSYSTEM=="hid", ACTION=="bind", RUN+="/usr/local/bin/changemouse.py"
+# XAUTHORUTY and DISPLAY must be set and related to the current session. It may
+# vary with different graphic drivers.
+SUBSYSTEM=="hid", ENV{DISPLAY}=":0", ENV{XAUTHORITY}="/run/user/1000/gdm/Xauthority", ACTION=="bind", RUN+="/usr/local/bin/changemouse.py"
 
 # the following line may not be needed as when we unplug a mouse it would
 # automatically remove devices from the list and they need no furthur