Fix: code detection logic in SearchResultMatch component
Created by: attfarhan
We relied on the markdown renderer to produce <code>
tags to wrap codeblocks
when rendering diff and commit results. Our markdown rendering changed, so this
is no longer the case (see https://github.com/sourcegraph/docsite/commit/a6c89266f4c141ee3b398737c9c4955379430278).
TODO: add tests for this so it doesn't break again. TODO: don't depend on the same markdown library as our docs site