move key/value wrapper function into anonymous namespace in ScriptingEnvironment

Extractor/ScriptingEnvironment.cpp

@@ -41,13 +41,14 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <osmium/osm.hpp>
 
 #include <sstream>
-
+namespace {
 // wrapper method as luabind doesn't automatically overload funcs w/ default parameters
 template<class T>
 auto get_value_by_key(T const& object, const char *key) -> decltype(object.get_value_by_key(key))
 {
     return object.get_value_by_key(key, "");
 }
+}
 
 ScriptingEnvironment::ScriptingEnvironment(const char *file_name)
 : file_name(file_name)