freebsd: fix capsicum warning

~~~
In file included from src/restrict_process_capsicum.c:16:                   /usr/include/sys/capability.h:44:2: warning: this file includes <sys/capability.h> which is deprecated [-W#warnings]
 ^
1 warning generated.
~~~

src/restrict_process_capsicum.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2017, Michael Santos <michael.santos@gmail.com>
+/* Copyright (c) 2017-2020, Michael Santos <michael.santos@gmail.com>
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -13,7 +13,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 #ifdef RESTRICT_PROCESS_capsicum
-#include <sys/capability.h>
+#include <sys/capsicum.h>
 #include <sys/param.h>
 #include <sys/resource.h>
 #include <sys/time.h>