syntax bug in exception

[matteofrigo]

There's a minor bug that concerns the behaviour when the KeyError exception is raised in the parameter range check of the set_equal_parameter method in the DistributeModel class.

An error is raised, but not the correct one. The raised one is due to a syntax error in the string formatting. The parenthesis after the second " must be moved at the end of the expression.

I'll prepare a PR asap.

https://github.com/AthenaEPI/dmipy/blob/9bd7038ea93edbf9cced56a7ef6a0f19f25388c3/dmipy/distributions/distribute_models.py#L342

[matteofrigo]

Yay we celebrate issue # 100 !