Remove extra comma

[eliot-akira]

Before:

When HTML, 2.0 was released, it introduced..

After:

When HTML 2.0 was released, it introduced..

I wondered if the comma was intentional, but most likely not.

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[dz4k]

Thanks for the fix. The comma was added for indexing purposes, and was not intended to appear in the text itself.

As we are rewriting the book with a different markup language and toolchain, we ported your contribution to the rewritten version, and this PR will be closed.