corrected mnemonic namespaces

[f4bio]

this will get rid of all the psr-4 warnings.

Class MoneroIntegrations\MoneroPhp\mnemonic\dutch located in ./vendor/monero-integrations/monerophp/src/wordsets/dutch.ws.php does not comply with psr-4 autoloading standard. Skipping.
...

I suspect there is a reason, nobody as taken this task upon himself yet already?! (Just close this in that case, no worries ;) )