Cleanup header files for builds with gcc

src/client.cpp

@@ -2,7 +2,7 @@
 #include "definitions.hpp"
 #include "server.hpp"
 #include <cstdio>
-#include <strings.h>
+#include <cstring>
 #include <unistd.h>
 
 Client::Client() : sock(), serverAddr() {

src/server.cpp

 #include "server.hpp"
+#include <cstring>
 #include <definitions.hpp>
 #include <sys/socket.h>