pip3 version of preprocess_interface.py has incorrect line 84

[adadiehl]

pip3 version of preprocess_interface.py returns list, not string:
reads_base_name = args.vg_json_reads_file_name.split(".")[0:-1]
Resulting mismatched types in string concatenation at line 102 cause program to crash.
This appears to be fixed in the main repository:
reads_base_name = '.'.join(args.vg_json_reads_file_name.split(".")[0:-1])

Please release a patch to pip!