* pass --stdio flag to expert lsp server
expert requires --stdio to use stdio transport but the linter
definition launched it without the flag, so the server never
entered lsp mode
* handle client/registerCapability requests from lsp servers
some lsp servers like expert send a client/registerCapability
request after initialization to dynamically register capabilities,
if ale does not respond the server blocks and never processes
further messages like textDocument/didOpen
