Add <time.h> includes where appropiate

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

src/User.cpp

@@ -22,6 +22,7 @@
 #include <znc/Chan.h>
 #include <znc/Query.h>
 #include <math.h>
+#include <time.h>
 #include <algorithm>
 
 using std::vector;