Fix history diff viewing

[magopian]

Fixes #562

[magopian]

@glasserc this partially reverts what was done in f2e9326?w=1#diff-783a4918ddce584cff30089389577b76, I'm not sure why you made the change in the HistoryTable component, maybe I'm missing something?

To review this PR, I would recommend using the "no whitespace diff" trick: https://github.com/Kinto/kinto-admin/pull/563/files?w=1

The change is minimal, and consists of reverting the modifications to the markup made in the two commits mentioned in the description of #562.

[magopian]

I think I now understand why the change was made, and I need to find another way to fix it. Will ping you @glasserc whenever I have a solution.

[magopian]

Ok, I think I found a workaround to make flow happy, ping @glasserc.

[leplatrem]

you can post a screenshot to help figuring out the changes

[glasserc]

I was surprised to discover that a <table> can contain "zero or more" <tbody> elements, so I guess this is fine.

[magopian]

Yeah @leplatrem the fix makes it display the diff taking the whole width of the table, as it used to:

[leplatrem]

Excellent thanks :)