Fix lint issues in lib/fsext

[mstoykov]

works on #769

[codecov-commenter]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (856a767) 73.22% compared to head (d4b699e) 73.16%.
Report is 11 commits behind head on master.

❗ Current head d4b699e differs from pull request most recent head 327040d. Consider uploading reports for the commit 327040d to get more accurate results

Files	Patch %	Lines
lib/fsext/walk.go	14.28%	5 Missing and 1 partial ⚠️
output/cloud/output.go	0.00%	1 Missing and 1 partial ⚠️
api/server.go	50.00%	1 Missing ⚠️
js/compiler/compiler.go	66.66%	1 Missing ⚠️
lib/fsext/changepathfs.go	0.00%	1 Missing ⚠️
output/cloud/v1/data.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3482      +/-   ##
==========================================
- Coverage   73.22%   73.16%   -0.07%     
==========================================
  Files         267      265       -2     
  Lines       20083    20078       -5     
==========================================
- Hits        14706    14690      -16     
- Misses       4463     4470       +7     
- Partials      914      918       +4     

Flag	Coverage Δ
ubuntu	73.16% <42.85%> (-0.01%)	⬇️
windows	?

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