style ENSEMBL is not supported

[lydiayliu]

Caused by #760

Traceback (most recent call last):
  File "/usr/local/bin/moPepGen", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.8/site-packages/moPepGen/cli/__main__.py", line 92, in main
    args.func(args)
  File "/usr/local/lib/python3.8/site-packages/moPepGen/cli/generate_index.py", line 141, in generate_index
    proteome.dump_fasta(parth_proteome, source=args.reference_source)
  File "/usr/local/lib/python3.8/site-packages/moPepGen/aa/AminoAcidSeqDict.py", line 55, in dump_fasta
    record.infer_ids(source)
  File "/usr/local/lib/python3.8/site-packages/moPepGen/aa/AminoAcidSeqRecord.py", line 93, in infer_ids
    raise ValueError(f'style {style} is not supported')
ValueError: style ENSEMBL is not supported

Also --reference-source from the command line cannot overwrite values given in index, and as a result I could not test if #760 resolved issued with #758