CXX-995 CXX-1256 Fix pool example URI
CXX-995 CXX-1256 Fix pool example URI

Newer libmongoc has stricter connection string parsing.

acmorrow/mongo-cxx-driver,xdg/mongo-cxx-driver,mongodb/mongo-cxx-driver,xdg/mongo-cxx-driver,mongodb/mongo-cxx-driver,xdg/mongo-cxx-driver,acmorrow/mongo-cxx-driver,mongodb/mongo-cxx-driver,acmorrow/mongo-cxx-driver,xdg/mongo-cxx-driver,acmorrow/mongo-cxx-driver,mongodb/mongo-cxx-driver