Fixes get_transactions for a single transaction

When the results returned by the API is just one the gem was crashing
due to it was expecting an array and
response.body['MSG_S']['LISTADOMOVSCTA']['E'] contained a Hash.

To fix this I just checked the three scenarios:
- Empty transactions (nil)
- Single transaction (Hash)
- Multiple transactions (Array)
Bumped version
Merge pull request #1 from hopsor/fix-get-transactions

Fix get transactions