Proofreading: Change a usage of "specially" to "especially"

See PR godotengine/godot-docs#561. This file generates documentation touched by that PR, so must be changed to stay in sync.

I couldn't find any other usages in this repo that needed changing. I looked in all files matching *.cpp *.h *.md *.txt *.xml *.html *.rst.

doc/classes/AnimationPlayer.xml

@@ -381,7 +381,7 @@
 	</signals>
 	<constants>
 		<constant name="ANIMATION_PROCESS_PHYSICS" value="0">
-			Process animation during the physics process. This is specially useful when animating physics bodies.
+			Process animation during the physics process. This is especially useful when animating physics bodies.
 		</constant>
 		<constant name="ANIMATION_PROCESS_IDLE" value="1">
 			Process animation during the idle process.