click seems to need string message

[bernt-matthias]

The current code causes a stack trace for some calls, eg.

enasearch retrieve_taxons --ids 'Elusimicrobia:phylum' --result 'coding_release' --display 'fasta' --download 'fasta' (probably the call is missing something anyway .. I'm just starting to explore this tool)

click wants to call encode() on the exception message (if python2 is used which is the case in Galaxy installations of enasearch):

https://github.com/pallets/click/blob/132d66ac7d69a2b0e8f218a4cd39e50be3e0bcb9/click/exceptions.py#L15

but an Exception is used as parameter:

https://github.com/bebatut/enasearch/blob/7c1e2806a81a58f86da4145834ea7200514b281b/enasearch/cli.py#L20