Update api.py

[si-bremer-enbw]

Updated default verify in Client class to True (instead of None)

The line "self.verify = True if verify else False" takes verify, if it is None, the result of this if clause will be False. Verify false is a bad default, disabling SSL verification as a default is a bad security practice.

[FussyDuck]

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[akeeman]

This pr is related to https://github.com/ecmwf/cdsapi/pull/39

[EddyCMWF]

This has been addressed by #64