[dev] Replace istanbul with nyc

Bắt đầu với lệnh grunt test và tìm dependency Istanbul cùng cấu hình coverage được CLI sử dụng. Kiểm tra cách bản build Jenkins nhận các lỗi kiểm thử và xác minh quá trình migration bằng ví dụ destructuring hiện đang gây ra lỗi cú pháp. Hoàn tất khi các kiểm thử chạy với nyc và lỗi coverage tạo ra trạng thái khác không.

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.