expected::operator*() for rvalue types should not be const

[mikemccarty-vertex]

opentracing-cpp/3rd_party/include/opentracing/expected/expected.hpp

Line 668 in 6fc9fac

constexpr value_type && operator *() const &&

E.g.

expected<Thing> get_expected_thing() { return ...; }

Thing t = *get_expected_thing();

... will fail to compile as currently written.