audio: fix imports for unsupported writers

[200sc]

This fixes a compilation error when building the audio package for non-windows/linux/darwin targets.

Pending before merge:

• [x] Trivial 'does this compile' tests for js for all examples.

[codecov-commenter]

Codecov Report

Merging #210 (0251eea) into master (df66d92) will decrease coverage by 0.06%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #210      +/-   ##
==========================================
- Coverage   95.02%   94.95%   -0.07%     
==========================================
  Files         143      143              
  Lines        6346     6346              
==========================================
- Hits         6030     6026       -4     
- Misses        285      287       +2     
- Partials       31       33       +2     

Impacted Files	Coverage Δ
collision/rtree.go	97.90% <0.00%> (-1.40%)	:arrow_down:

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[200sc]

( The windows builder machine is powered off and won't take the job. )