Merge branch 'bugfix/build-failure-on-i386' into 'master'

Use correct type for second template argument of `std::array`

See merge request !90

dune/istl/io.hh

@@ -599,7 +599,7 @@ namespace Dune {
   }
 
   // Recursively print all the blocks -- specialization for std::array
-  template<class K, unsigned long n>
+  template<class K, std::size_t n>
   void writeVectorToMatlabHelper (const std::array<K,n>& v, std::ostream& s)
   {
     for (const auto& entry : v)