Missing header file

Author: piermarcobarbe

src/Core.cpp

@@ -14,6 +14,7 @@
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <unistd.h>
 #include <iostream>
 #include <cstring>
 #include <zconf.h>
@@ -218,4 +219,4 @@ void Core::releasePool() {
  delete slot;
  usleep(5000);
  }
-}
+}