Future compatibility warning

[Peter Atashian]

   Compiling reg-watcher v0.1.0
warning[E0382]: assign to part of moved value: `self`
   --> C:\Users\appveyor\.cargo\registry\src\github.com-1ecc6299db9ec823\reg-watcher-0.1.0\src\lib.rs:282:9
    |
260 |         mut self,
    |         -------- move occurs because `self` has type `Watcher`, which does not implement the `Copy` trait
...
267 |         let handle = builder.spawn(move || {
    |                                    ------- value moved into closure here
...
271 |                     self.notify_filter,
    |                     ---- variable moved due to use in closure
...
282 |         self.handle = Some(handle);
    |         ^^^^^^^^^^^ value partially assigned here after move
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
    = note: for more information, try `rustc --explain E0729`

[Liu BoFan]

Fixed, thanks for reminding me.