Add ctime header to vodus main

Regarding compilation issues in FreeBSD. The <time.h> header is not
automatically pulled in on FreeBSD. Might be a quirk in glibc.

src/vodus.cpp

@@ -2,6 +2,7 @@
 #include <cstdio>
 #include <cstdint>
 #include <cmath>
+#include <ctime>
 
 #include <algorithm>