Syntax error in BIFXML export

When saving a Bayesian network to the BIFXML format, the following comment is inserted:

<!- OUTCOME are not used in pyAgrum BIFXML (see fast property) but are kept for compatibility->

However, this comment is not properly formatted: it should start with <!-- and end with ->. For this reason, I cannot parse the file with my software.

I propose a merge request, as it is a trivial change.