Fixed call to checkToken after reconnection

[xbill82]

Fixes a call to checkToken upon reconnection to Kuzzle. The previous version was surely a copy/paste error based on v5.

How should this be manually tested?

• connect to Kuzzle
• add a listener on the reconnected event
• disconnect from Kuzzle (one way to do it is to docker-compose stop kuzzle)
• reconnect to Kuzzle
• the callback attached to your listened should be triggered

[scottinet]

Is it possible to add a unit test?

[xbill82]

@scottinet yep, sorry I forgot to add the WIP tag... Just added the test!

[codecov-io]

Codecov Report

Merging #359 into 6-dev will decrease coverage by 0.13%.
The diff coverage is 75%.

@@            Coverage Diff             @@
##            6-dev     #359      +/-   ##
==========================================
- Coverage   96.59%   96.45%   -0.14%     
==========================================
  Files          28       28              
  Lines        1409     1411       +2     
==========================================
  Hits         1361     1361              
- Misses         48       50       +2

Impacted Files	Coverage Δ
src/Kuzzle.js	94.93% <75%> (-0.89%)	⬇️

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