Fix document create

[Aschen]

What does this PR do ?

Autogenerate ID for when creating document without specifying ID.

Fix https://github.com/kuzzleio/sdk-php/issues/102

How should this be manually tested?

• Step 1 : Create index myindex and collection mycollection
• Step 2 : Run this script twice:

  
  <?php
  include __DIR__ . '/tests/bootstrap.php';

$kuzzle = new \Kuzzle\Kuzzle('localhost');

$collection = 'mycollection'; $index = 'myindex';

// enabling auto refresh (avoiding sleep between add/deletion and search) $kuzzle->setAutoRefresh($index);

$collection = $kuzzle->collection($collection, $index);

// add a document print_r('add a document'); print_r("\n"); $document = $collection->createDocument(['foo' => 'bar']); print_r($document->serialize());

### Other changes

 - Add a docker-compose file for development (See this PR for custom image https://github.com/kuzzleio/kuzzle-containers/pull/47)

[codecov-io]

Codecov Report

Merging #103 into 3-dev will increase coverage by 0.01%. The diff coverage is 100%.

@@           Coverage Diff            @@
##            3-dev   #103      +/-   ##
========================================
+ Coverage   90.98%    91%   +0.01%     
========================================
  Files          15     15              
  Lines        1498   1500       +2     
========================================
+ Hits         1363   1365       +2     
  Misses        135    135

Impacted Files	Coverage Δ
src/Collection.php	91.72% <ø> (ø)	:arrow_up:
src/Kuzzle.php	91.25% <100%> (+0.04%)	:arrow_up:

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