Fix a spelling error

docs/api/en/materials/Material.html

@@ -278,7 +278,7 @@
 		as transparent objects need special treatment and are rendered after
 		non-transparent objects. <br />
 		When set to true, the extent to which the material is transparent is
-		controlled by setting it's [page:Float opacity] property. <br />
+		controlled by setting its [page:Float opacity] property. <br />
 		Default is *false*.
 		</p>