Should use a coercion instead of GRing.Linear.apply

[CohenCyril]

coq-robot/differential_kinematics.v

Lines 222 to 223 in 8266510

	Lemma differential_cross_product (v : 'rV[R^o]_3) y :
	GRing.Linear.apply ('d_y (fun x => v *v x)) = GRing.Linear.apply (mx_lin1 \S( v )).

'd_y (fun x => v *v x) = mx_lin1 \S( v ) :> _ -> _.