Fix `bevy_text` plugin registration (#72)

Fix registration of the `component_animator_system::<Text>` in the
`TweeningPlugin` to depend on the new `bevy_text` feature, and not on
the `bevy_ui` one.

src/plugin.rs

@@ -44,8 +44,7 @@ impl Plugin for TweeningPlugin {
         );
 
         #[cfg(feature = "bevy_ui")]
-        app.add_system(component_animator_system::<Text>.label(AnimationSystem::AnimationUpdate))
-            .add_system(component_animator_system::<Style>.label(AnimationSystem::AnimationUpdate));
+        app.add_system(component_animator_system::<Style>.label(AnimationSystem::AnimationUpdate));
 
         #[cfg(feature = "bevy_sprite")]
         app.add_system(component_animator_system::<Sprite>.label(AnimationSystem::AnimationUpdate));
@@ -54,6 +53,9 @@ impl Plugin for TweeningPlugin {
         app.add_system(
             asset_animator_system::<ColorMaterial>.label(AnimationSystem::AnimationUpdate),
         );
+
+        #[cfg(feature = "bevy_text")]
+        app.add_system(component_animator_system::<Text>.label(AnimationSystem::AnimationUpdate));
     }
 }