rename file /tests/data/data.h5 as /tests/data/demography.h5

[alixdamman]

and update example.py

[alixdamman]

use os.path.join(EXAMPLE_FILES_DIR, 'demography.h5') instead of simple +

[thelazyoxymoron]

@alixdamman Hi! I would like to take up this issue.