Fix compile error

At least on my system (Fedora 28) gcc gave a compile error for std::vector being used here despite being undefined.
Adding the appropriate include fixes the problem, and seems unlikely to cause any other problems.

src/slic3r/GUI/KBShortcutsDialog.hpp

@@ -3,6 +3,7 @@
 
 #include <wx/wx.h>
 #include <map>
+#include <vector>
 
 namespace Slic3r { 
 namespace GUI {