Update hello_audio.adoc

Fixed broken horizontal rule.

src/docs/asciidoc/jme3/beginner/hello_audio.adoc

@@ -345,6 +345,7 @@ You now know how to add the two most common types of sound to your game: Global
 *Tip:* JME's Audio implementation also supports more advanced effects such as reverberation and Doppler effect. Use these “pro features to make audio sound different depending on whether it's in the hallway, in a cave, outdoors, or in a carpeted room. Find out more about environmental effects from the sample code included in the jme3test directory and from the advanced <<jme3/advanced/audio#,Audio>> docs.
 
 Want some fire and explosions to go with your sounds? Read on to learn more about <<jme3/beginner/hello_effects#,effects>>.
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 See also: