Update variable description on upsert

[csk1827]

Fixes #740

Issue

Variable description is not updating on upsert.

const list = new VariableList(null, [{
    key: 'k1',
    value: 'initial',
    description: 'initial description'
}]);

list.upsert({
    key: 'k1',
    value: 'updated',
    description: 'updated description'
});

list.toJSON();
// [{
//     description: {
//         content: 'initial description',
//         type: 'text/plain'
//     },
//     type: 'any',
//     value: 'updated',
//     key: 'k1'
// }]

Fix

Update description also on variable upsert.

Validation

Changes validated locally.

[csk1827]

@codenirvana @shamasis please review the PR

[codecov[bot]]

Codecov Report

Merging #998 into develop will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #998   +/-   ##
========================================
  Coverage    96.87%   96.88%           
========================================
  Files           39       39           
  Lines         2369     2372    +3     
  Branches       703      704    +1     
========================================
+ Hits          2295     2298    +3     
  Misses          74       74           

Flag	Coverage Δ
#unit	96.88% <100.00%> (+<0.01%)	:arrow_up:

Impacted Files	Coverage Δ
lib/collection/variable.js	96.73% <100.00%> (+0.10%)	:arrow_up:

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[csk1827]

@codenirvana added the unit tests for the changes made

[codenirvana]

deferring because the same issue is present in other Property.

[codenirvana]

Closing in favor of #1332