chore: use new form of octal

[wolfogre]

Go 1.13 added the 0o form for octal numbers, like 0o644, it's more readable than 0644.

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Just a suggestion, please feel free to close this PR if you think it's unnecessary.

[codecov]

Codecov Report

Merging #1630 (0c066c7) into master (4989f44) will increase coverage by 0.70%.
The diff coverage is 75.30%.

@@            Coverage Diff             @@
##           master    #1630      +/-   ##
==========================================
+ Coverage   61.22%   61.92%   +0.70%     
==========================================
  Files          46       46              
  Lines        7141     7249     +108     
==========================================
+ Hits         4372     4489     +117     
+ Misses       2462     2457       -5     
+ Partials      307      303       -4     

Impacted Files	Coverage Δ
pkg/container/docker_cli.go	82.23% <ø> (ø)
pkg/container/docker_logger.go	52.08% <ø> (ø)
pkg/container/docker_pull.go	33.33% <ø> (ø)
pkg/container/docker_run.go	13.58% <ø> (ø)
pkg/container/docker_volume.go	0.00% <ø> (ø)
pkg/container/file_collector.go	39.68% <0.00%> (+2.38%)	⬆️
pkg/container/host_environment.go	0.00% <0.00%> (ø)
pkg/container/docker_images.go	27.02% <29.41%> (-4.13%)	⬇️
pkg/model/github_context.go	61.06% <32.00%> (-19.40%)	⬇️
pkg/container/docker_auth.go	51.35% <56.25%> (+3.73%)	⬆️
... and 22 more

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[ChristopherHX]

I'm open to change the octal literal syntax