Fix npm test command in README.md

[ravioliss]

Corrected the npm test command syntax in the README.

Because

with out the two dash it was giving me a fail test knowing it was right.

This PR

the comand do not include the two dashed before the file.

Issue

Closes #XXXXX

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the location of change: brief description of change format, e.g. 01_helloWorld: Update test cases
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If this PR includes any changes that affect the solution of an exercise, I've also updated the solution in the /solutions folder

[mao-sz]

Could you share a screenshot of your terminal showing the location, the command npm test helloWorld.spec.js (no double dash), and the full error output please?