Fix for bug of the function is_json_mimetype()

[jacobstanly89]

Fixes #1114

Changes proposed in this pull request:

• In the file connexion/utils.py, under function is_json_mimetype() the following has been added to take into account the ';' that might be present in the mimetype

if ';' in subtype: subtype, parameter = subtype.split(';')

• Added the corresponding tests in tests/test_utils.py

[Ruwann]

Thanks for the PR!

Could you also add a test for this? It can be added in tests/test_utils.py

[coveralls]

Pull Request Test Coverage Report for Build 2416476643

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 94.342%

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Totals
Change from base Build 2379282948:	0.004%
Covered Lines:	2651
Relevant Lines:	2810

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💛 - Coveralls

[Ruwann]

Thanks a lot, @jacobstanly89 !