support face colors when writing in OpenInventor format

src/Mod/Part/App/TopoShapePy.xml

@@ -33,7 +33,7 @@ Sub-elements such as vertices, edges or faces are accessible as:
         <UserDocu>Read in an IGES, STEP or BREP file.</UserDocu>
       </Documentation>
     </Methode>
-    <Methode Name="writeInventor" Const="true">
+    <Methode Name="writeInventor" Const="true" Keyword="true">
       <Documentation>
         <UserDocu>Write the mesh in OpenInventor format to a string.</UserDocu>
       </Documentation>