Moved strategy of one level in request object

[jenow]

According to new login in Kuzzle strategy is not part of the body anymore but in the upper level of the request:

{
  body: {
    username: 'foo',
    password: 'bar'
  },
  strategy: 'local'
}

[codecov-io]

Codecov Report

Merging #221 into 4.x will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             4.x     #221      +/-   ##
=========================================
+ Coverage   99.4%   99.45%   +0.05%     
=========================================
  Files         16       16              
  Lines       1845     1845              
  Branches     529      529              
=========================================
+ Hits        1834     1835       +1     
+ Misses        11       10       -1

Impacted Files	Coverage Δ
src/Kuzzle.js	99.66% <100%> (+0.16%)	⬆️

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[scottinet]

Changed target branch to 5.x

[scottinet]

Changes proposed by this pull request are already there in the 5.x branch. I'm closing this PR.