Bump flask to be at least 1.0.4

[kornicameister]

Fixes #991 .

Changes proposed in this pull request:

• bump flask to be at least 1.0.4

Reasons:

• flask==0.10.1 was released in 2013, which makes it quite old thus unsupported.
• On Flask webpage you can find an information pointing to 1.x branch as latest stable
• different tools, including these used in connexion progressed leaving Python versions, for which flask<1.0 has been developed.

[kornicameister]

cc @hjacobs

[kornicameister]

Hmm...

E       pytest.PytestDeprecationWarning: The 'message' parameter is deprecated.
E       (did you mean to use `match='some regex'` to check the exception message?)
E       Please see:
E         https://docs.pytest.org/en/4.6-maintenance/deprecations.html#message-parameter-of-pytest-raises

but that's unrelated to flask change. I guess we gotta change some tests as well to use this match.
I will create another issue and fix'em in separate PR to make changes atomic. Though, it might be needed to bump pytest. For Python2.7 older version of pytest is being installed which does not emit this error.

@hjacobs any suggestions as how to proceed with that?

[hjacobs]

Does it work when switching to the match parameter?

[kornicameister]

@hjacobs it passed for 2.7, 3.4, 3.5, 3.6 and 3.7 versions. Should I just add the changes to this PR?

[hjacobs]

@kornicameister yes

[kornicameister]

@hjacobs it went perfectly ok :)

[hjacobs]

@kornicameister thanks!

[hjacobs]

👍