[DOCS] minor ParticlesMaterial docs fix Linear -> Radial

doc/classes/ParticlesMaterial.xml

@@ -132,7 +132,7 @@
 			Orbital velocity randomness ratio. Default value: [code]0[/code].
 		</member>
 		<member name="radial_accel" type="float" setter="set_param" getter="get_param">
-			Linear acceleration applied to each particle.
+			Radial acceleration applied to each particle.
 		</member>
 		<member name="radial_accel_curve" type="Texture" setter="set_param_texture" getter="get_param_texture">
 			Each particle's radial acceleration will vary along this [CurveTexture].