process_collector: fix compilation on 32-bit targets (#446)

The crate didn't compile on 32-bit targets any more due to
libc::sysconf() returning a 32-bit value on those targets.

Signed-off-by: Frank Denis <github@pureftpd.org>

src/process_collector.rs

@@ -190,14 +190,14 @@ lazy_static! {
     static ref CLK_TCK: i64 = {
         unsafe {
             libc::sysconf(libc::_SC_CLK_TCK)
-        }
+        }.into()
     };
 
     // getconf PAGESIZE
     static ref PAGESIZE: i64 = {
         unsafe {
             libc::sysconf(libc::_SC_PAGESIZE)
-        }
+        }.into()
     };
 }