Update mocha.js to correct typos

[MystK]

Corrected two typos

[mousetraps]

Thanks for the PR. I know it's a small change, but would you mind signing https://cla.microsoft.com/? For future PRs, the request will be automatic... so kudos for making a PR before we even set that up. 😃

[msftclas]

@MystK, Thanks for signing the contribution license agreement so quickly! Actual humans will now validate the agreement and then evaluate the PR.

Thanks, MSBOT;

[ASayre]

Looks good to me!