Update README.md

[victim-alt]

Fixing few typos in the README.md for improving the documentation of the project.

• [ Y] Have you followed the guidelines in our Contributing document?
• [ Y] Have you checked to ensure there aren't other open Pull Requests for the same change?
• [ Y] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ NA] Have you written new tests for your changes? Here's an example.
• [ NA] Have you successfully run brew style with your changes locally?
• [ NA] Have you successfully run brew typecheck with your changes locally?
• [ NA] Have you successfully run brew tests with your changes locally?

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[p-linnane]

These are correct in Commonwealth English. The proposed changes are American English. Our guidelines state that we prefer British/Commonwealth English.