Fixed missing includes of the standard library (vector & iostream) so that we...

Fixed missing includes of the standard library (vector & iostream) so that we can compile with clang

src/limbo/init/random_sampling.hpp

 #ifndef LIMBO_INIT_RANDOM_SAMPLING_HPP
 #define LIMBO_INIT_RANDOM_SAMPLING_HPP
 
+#include <iostream>
 #include <Eigen/Core>
 
 #include <limbo/tools/rand.hpp>

src/limbo/model/gp.hpp

@@ -4,6 +4,7 @@
 #include <iostream>
 #include <cassert>
 #include <limits>
+#include <vector>
 
 #include <Eigen/Core>
 #include <Eigen/LU>