Jest/istanbul.js coverage HTML report bug

Steps to reproduce: (https://jestjs.io/docs/en/getting-started)

• Create a new folder
• Init a new npm project with npm init
• Add Jest as a dependency npm install --save-dev jest
• Created a src folder with a main.js file and a main.spec.js test file (one containing sum function and the other the tests as in the Jest docs)
• Added a test script in package.json.
• Run the script with npm test -- --coverage