Fix compilation in rust 1.38
Fixes this error when compiling:
```
error[E0282]: type annotations needed
--> ~/.cargo/registry/src/github.com-1ecc6299db9ec823/fruitbasket-0.8.0/src/osx.rs:589:13
|
589 | / msg_send![manager,
590 | | setEventHandler: objc
591 | | andSelector: sel!(handleEvent:withReplyEvent:)
592 | | forEventClass: class
593 | | andEventID: id];
| | ^
| | |
| |______________________________________________cannot infer type
| consider giving `result` a type
|
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: aborting due to previous error
```
let cls = Class::get("NSAppleEventManager").unwrap();
let manager: *mut Object = msg_send![cls, sharedAppleEventManager];
let objc = (*self.objc).take();
- let _ = msg_send![manager,
+ let _:() = msg_send![manager,
setEventHandler: objc
andSelector: sel!(handleEvent:withReplyEvent:)
forEventClass: class