Use older version of biopython.

[digithed]

biopython versions newer than 1.7.7 seem to cause the following error with the synbio library:

"ImportError: Bio.Alphabet has been removed from Biopython. In many cases, the alphabet can simply be ignored and removed from scripts. In a few cases, you may need to specify the molecule_type as an annotation on a SeqRecord for your script to work correctly. Please see https://biopython.org/wiki/Alphabet for more information."

In the future the code should be refactored to remove using Bio.Alphabet although for now I'm fixing the biopython version to get things back to working order.