allow trailing \ for DayOne journals

https://github.com/maebert/jrnl#dayone-integration
sort of infers that it in the .jrnl_config it should end in a /

but prior to this, if there was a trailing / then jrnl thought it was
looking at a text type journal.
Merge pull request #61 from alapolloni/master

Update jrnl.py so that a trailing / for a DayOne journal config is seen as a DayOne journal.