[dev] Replace istanbul with nyc

grunt test コマンドから始め、CLI で使用されている Istanbul 依存関係とカバレッジ設定を見つけてください。Jenkins ビルドがテストの失敗をどのように受け取るかを確認し、現在構文エラーを引き起こしている destructuring の例に対して移行を検証してください。テストが nyc で実行され、カバレッジエラーがゼロ以外のステータスを生成すれば完了です。

As the istanbul package is not longer maintained, we need to migrate to nyc.
Currently istanbul doesn't work for the following code:

const { stdio = "inherit" } = options;

In this case grunt test command fails with an exception:

__cov_gCRxMpJElFAq6oDSOHYQNQ.s['1']++;var __awaiter=(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['1'][0]++,this)&&(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['1'][1]++,this.__awaiter)||(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['1'][2]++,function(thisArg,_arguments,P,generator){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['1']++;__cov_gCRxMpJElFAq6oDSOHYQNQ.s['2']++;return new((__cov_gCRxMpJElFAq6oDSOHYQNQ.b['2'][0]++,P)||(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['2'][1]++,P=Promise))(function(resolve,reject){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['2']++;function fulfilled(value){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['3']++;__cov_gCRxMpJElFAq6oDSOHYQNQ.s['4']++;try{__cov_gCRxMpJElFAq6oDSOHYQNQ.s['5']++;step(generator.next(value));}catch(e){__cov_gCRxMpJElFAq6oDSOHYQNQ.s['6']++;reject(e);}}function rejected(value){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['4']++;__cov_gCRxMpJElFAq6oDSOHYQNQ.s['8']++;try{__cov_gCRxMpJElFAq6oDSOHYQNQ.s['9']++;step(generator['throw'](value));}catch(e){__cov_gCRxMpJElFAq6oDSO

SyntaxError: Unexpected token :
    at new Script (vm.js:79:7)
    at createScript (vm.js:251:10)
    at Object.runInThisContext (vm.js:303:10)
    at Module._compile (internal/modules/cjs/loader.js:656:28)
    at Object.Module._extensions.(anonymous function) [as .js] (/Users/havaluova/Work3/nativescript-cli/node_modules/istanbul/lib/hook.js:107:24)
    at Module.load (internal/modules/cjs/loader.js:598:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:537:12)
    at Function.Module._load (internal/modules/cjs/loader.js:529:3)
    at Module.require (internal/modules/cjs/loader.js:636:17)
    at require (internal/modules/cjs/helpers.js:20:18)

It seems that when the above mentioned error occurs, istanbul exits with status code 0 and this is the reason why jenkins build doesn't fail in such situation.