Update index.bs

Co-authored-by: Reilly Grant <[email protected]>

index.bs

@@ -62,7 +62,7 @@ This specification provides two new DOM events for obtaining information about t
 
 The {{deviceorientation}} event represents the physical orientation of the device, expressed as a series of rotations from a local coordinate frame.
 
-The {{devicemotion}} represents the acceleration of the device, expressed in Cartesian coordinates in a coordinate frame defined in the device. It also supplies the rotation rate of the device about a local coordinate frame. Where practically possible, the event should provide the acceleration of the device's center of mass.
+The {{devicemotion}} event represents the acceleration of the device, expressed in Cartesian coordinates in a coordinate frame defined in the device. It also supplies the rotation rate of the device about a local coordinate frame. Where practically possible, the event should provide the acceleration of the device's center of mass.
 
 The following code extracts illustrate basic use of the events.