Modify the find-migrations function to support multiple migrations directories.
The :migration-dir param could be a string (as it was before) or it could be a vector of strings and the find-migrations function collects migrations from all the directories specified
Modify the find-migrations function to support multiple migrations directories. The :migration-dir param could be a string (as it was before) or it could be a vector of strings and the find-migrations function collects migrations from all the directories specified