Wrong formatting of MaxAllowedMolecules accepted in config file

[VGPReys]

Describe the bug
String is not formatted when Exception is thrown.

To Reproduce
Put 50 input molecules at once in the configuration file:
molecules = ['mol1.pdb', ..., 'mol50.pdb']

raise ConfigurationError("Too many molecules defined, max is {max_molecules_allowed}.")

Expected behavior
Should return the value of max_molecules_allowed instead of the variable name

Additional context (optional - remove if not relevant)
I will solve this soon, this is just to keep track