use mutable lambda in wrapper

This allows passing in mutable lambda expressions or other function
objects having a non-`const` `operator()`.

dune/solvers/solvers/criterion.hh

@@ -78,7 +78,7 @@ namespace Dune {
       template<class F,
         std::enable_if_t<std::is_convertible<std::result_of_t<F()>, std::string>::value, int> = 0>
       Criterion(F&& f, const std::string& header) :
-        f_( [=]() {return std::make_tuple(false, f());} ),
+        f_( [=]() mutable {return std::make_tuple(false, f());} ),
         header_(header)
       {}