fix build warnings

And in Travis CI, treat warnings as error
to keep from merging codes with warning.

Fixes: #13

Signed-off-by: bin liu <bin@hyper.sh>

src/cpu.rs

@@ -111,7 +111,8 @@ impl<'a> From<&'a Subsystem> for &'a CpuController {
                 Subsystem::Cpu(c) => c,
                 _ => {
                     assert_eq!(1, 0);
-                    ::std::mem::uninitialized()
+                    let v = std::mem::MaybeUninit::uninit();
+                    v.assume_init()
                 }
             }
         }