Example helper function for printing vectors should use passed std::ostream instead of std::cout

[Grigory Sokolov <greg.sokolov@…>]

Affected files: example/multiple_sources.cpp, example/options_description.cpp

template<class T> ostream& operator<<(ostream& os, const vector<T>& v) {

copy(v.begin(), v.end(), ostream_iterator<T>(cout, " ")); return os;

}

should be replaced with

template<class T> ostream& operator<<(ostream& os, const vector<T>& v) {

copy(v.begin(), v.end(), ostream_iterator<T>(os, " ")); return os;

}

[Vladimir Prus]

(In [77826]) Make vector print function in examples be more correct. Fixes #6677.