Fix missing include

lib/base/dictionary.cpp

@@ -22,6 +22,7 @@
 #include "base/debug.hpp"
 #include "base/primitivetype.hpp"
 #include "base/configwriter.hpp"
+#include <sstream>
 
 using namespace icinga;
 

lib/base/process.hpp

@@ -25,6 +25,7 @@
 #include <iosfwd>
 #include <deque>
 #include <vector>
+#include <sstream>
 
 namespace icinga
 {