dircolors change: add default coloring for opus audio files

[Scott Teal]

Hello,

I'm asking for a relatively minor improvement. The Opus audio codec now 
has its own entry on 
https://wiki.xiph.org/index.php/MIME_Types_and_File_Extensions, so I am 
requesting that it be added to the list in src/dircolors.hin. It just 
needs to be appended to the end of dircolors.hin as ".opus 00;36".

Thank you,
Scott Teal