shorten topic

docs/modules/core/nav.adoc

@@ -25,7 +25,7 @@
 *** xref:animation/animation.adoc[Animation]
 *** xref:cinematic/cinematics.adoc[Cinematics (cutscenes, fake destruction physics)]
 *** xref:cinematic/motionpath.adoc[MotionPaths and Waypoints]
-** Materials, Light, Shadow
+** Material, Light, Shadow
 *** xref:material/how_to_use_materials.adoc[How to use Materials]
 *** xref:material/j3m_material_files.adoc[.j3m Material Files]
 *** xref:material/material_definitions.adoc[.j3md Material Definitions]
@@ -37,7 +37,7 @@
 *** xref:texture/anisotropic_filtering.adoc[Anisotropic Filtering]
 *** xref:system/jme3_srgbpipeline.adoc[Gamma Correction]
 ** Audio, Video
-*** xref:audio/audio.adoc[Audio: Playing Sounds]
+*** xref:audio/audio.adoc[Playing Sounds]
 *** xref:audio/audio_environment_presets.adoc[Audio Environment Presets]
 *** xref:app/state/screenshots.adoc[Capture Screenshots]
-*** xref:app/state/capture_audio_video_to_a_file.adoc[Capture Audio/Video to a File]
+*** xref:app/state/capture_audio_video_to_a_file.adoc[Capture Audio/Video to File]