ConstReferenceGenerator enters the reference_name not as string into the env

[bhk11]

The ConstReferenceGenerator has the issue that the name of the reference value, e.g. 'torque', is not saved as string into env.reference_names during the initialization of the gem environment with gem.make. The string is saved in single characters into the reference_names, e.g. ['t','o','r','q','u','e'].

Used version: gym-electric-motor v1.1.0