Beautiful will does not parse HTML entities like `'` as we expect
and the previous logic of replacing this *after* HTML parsing occurred
did not produced expected results.
To illustrate this, we change data in "test_timeline" to include a
literal `'` as it sometimes occur in data returned by Mastodon API.
New HTML content is:
<p>The computer can't tell you the emotional story [...] </p>
Beautiful will parse this as as:
<p>The computer can&apost tell you the emotional story [...] </p>
which is not what we expect.
We fix this by replacing `'` *before* HTML parsing by Beautiful.
Since test data in "test_timeline" got updated we also add an extra
assertion checking that part of the content with a literal "'" is
(still) properly rendered.