pointer-gestures: correct description of pinch

This is being picky, but "pinch/spread" is the physical gesture, zoom and
rotate is the effect that clients provide in response to that gesture.
Let's use pinch only here since spread is more ambiguous in english, as anyone
who's ever had butter on their bread would know.

Also, everything else is referring to it as pinch anyway, so zoom/rotate here
is the odd one out.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

unstable/pointer-gestures/pointer-gestures-unstable-v1.xml

@@ -6,7 +6,7 @@
       A global interface to provide semantic touchpad gestures for a given
       pointer.
 
-      Two gestures are currently supported: swipe and zoom/rotate.
+      Two gestures are currently supported: swipe and pinch.
       All gestures follow a three-stage cycle: begin, update, end and
       are identified by a unique id.