Insert semicolon to ensure whitespace is not significant

[johno]

For large documents Babel will deopt styling which can
cause whitespace to change. When this happens we can result
in something like:

/* ... */;}MDXContent.isMDXComponent=true/* ... */

This will result in invalid syntax that causes the document
to break builds. With an explicit semicolon that will no
longer happen.

Closes #618

[vercel]

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