Fix a "no such file or directory" in src2bin.py
Created by: valeriodean
After downloaded and unzipped leeno-master.zip, there wasn't any "bin" directory in leeno-master, thus the src2bin.py failed with the error: IOError: [Errno 2] No such file or directory: 'bin/Ultimus.oxt' Check if the directory "bin" exists, if not, creates it.
Tested locally, the file "Ultimus.oxt" is correctly created inside the "bin" dir.