Update __main__.py

sqlite3.ProgrammingError: SQLite objects created in a thread can only be used in that same thread.
I'm not sure if it is without risk though.

https://github.com/g2p/bedup/issues/38
https://github.com/cxcv/bedup/commit/62ec8dd5df54731e0eb94cf39b06743e48998ba2