Fix compatibility with newer flask-login

[Malizor]

In requirements.txt, we have the following: flask-login<=0.2.11.

As far as I know, this was supposed to be a temporary measure because of upstream problems with the 0.3.0 version (see #89). But now, the latest upstream version is 0.4.1.

cve-search should be patched so that the requirement can be bumped to follow upstream again.
I suggest to not require more than 0.4.0 for now, as this is the version available in Debian Stretch and Ubuntu 18.04.

[PidgeyL]

Good point. Have you already tested if they are compatible or need code changes?

[Malizor]

So it was last year, but as far as I remember it did not work out of the box.
I have no idea of the amount of work required.

[PidgeyL]

I'll check it out

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