Fix CI, travis version, documentation version and snippets on 3-dev

[Shiranuit]

What does this PR do?

• Fix CI docker-compose that was working with Kuzzle V1 and not Kuzzle V2
• Update doc snippets version from 1 to 3
• Fix snippets that were broken, and not detected because of a bug in the CI docker-compose
• Update travis version from 1.14.x to 1.15.x

[codecov]

Codecov Report

Merging #274 (5e9fc1b) into 3-dev (26bf670) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            3-dev     #274      +/-   ##
==========================================
+ Coverage   89.58%   89.71%   +0.12%     
==========================================
  Files         240      241       +1     
  Lines        4024     4034      +10     
==========================================
+ Hits         3605     3619      +14     
+ Misses        367      365       -2     
+ Partials       52       50       -2     

Impacted Files	Coverage Δ
collection/refresh.go	100.00% <100.00%> (ø)
collection/update_specifications.go	100.00% <100.00%> (+9.09%)	⬆️
collection/validate_specifications.go	71.42% <100.00%> (+3.42%)	⬆️
document/update.go	100.00% <100.00%> (ø)
index/mDelete.go	90.90% <100.00%> (+1.43%)	⬆️

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