use inspect instead of join to stringify arrays

[tequeter]

Less hand-coding and more readable for long ACLs, IMHO.

Before:

current_value , should be user:hrref:rwx,default:user:hrref:rwx,...

After:

current_value [], should be ["user:hrref:rwx", "default:user:hrref:rwx", ...

[tequeter]

Just as PR #28, the Travis build fails because of dependencies not compatible with old Ruby versions. This is unrelated to my PR AFAICT.

Gem::InstallError: rake requires Ruby version >= 1.9.3.
Gem::InstallError: json_pure requires Ruby version ~> 2.0.
etc.

[roidelapluie]

Thanks!