[TD] change RichAnnos's linestyle to the one of other TD components

we already use enumerations for line styles for other components of TD and also the preferences. It seems I just have overseen this occurrence.

src/Mod/TechDraw/Gui/ViewProviderLeader.cpp

@@ -208,7 +208,7 @@ double ViewProviderLeader::getDefLineWeight(void)
 }
 
 App::Color ViewProviderLeader::getDefLineColor(void)
-{
+{
     return PreferencesGui::leaderColor();
 }