Review and Improvement of gilded-rose-kata repo: Js code

[selma-belhadj]

What does this PR do?

• This PR is raised to review & improve the js code in this forked repo

Description of the task to be completed

• Suggest DRY, KISS, YAGNI pieces of code
• Suggest renaming variables and functions following the best practices of JS
• Suggest using let instead of var
• Suggest using forEach instead of for
• Define Item as a class instead of just function & define needed methods
• Add tests for item class methods using jest framework
• Add tests for updateQuality method using jest framework

How should it be tested

• clone the repository by running
  git clone https://github.com/CircleCI-Archived/gilded-rose-kata.git
• navigate to the folder
  cd gilded-rose-kata
• Install packages
  npm install
• Run the app
  npm start
• Run the test
  npm run test