Fix table::insert when called with const& arguments.
Fix table::insert when called with const& arguments.

cpptoml::valid_value<T> wasn't properly decaying T when checking for type
equality within the trait.

skystrife/cpptoml,Nephatrine/cpptoml,vadz/cpptoml,vadz/cpptoml,skystrife/cpptoml,Nephatrine/cpptoml