Fixed some compiler warnings

src/error.rs

@@ -25,7 +25,7 @@ impl StdError for Error {
         }
     }
 
-    fn cause(&self) -> Option<&StdError> {
+    fn cause(&self) -> Option<&dyn StdError> {
         match *self {
             Error::MenusNotSupported => None,
             Error::MenuExists(_) => None,

src/key_handler.rs

@@ -4,7 +4,7 @@ use std::mem;
 use {Key, KeyRepeat, InputCallback};
 
 pub struct KeyHandler {
-    pub key_callback: Option<Box<InputCallback>>,
+    pub key_callback: Option<Box<dyn InputCallback>>,
     prev_time: f64,
     delta_time: f32,
     keys: [bool; 512],
@@ -70,7 +70,7 @@ impl KeyHandler {
         }
     }
 
-    pub fn set_input_callback(&mut self, callback: Box<InputCallback>) {
+    pub fn set_input_callback(&mut self, callback: Box<dyn InputCallback>) {
         self.key_callback = Some(callback);
     }
 

src/lib.rs

@@ -512,7 +512,7 @@ impl Window {
     /// Set input callback to recive callback on char input
     ///
     #[inline]
-    pub fn set_input_callback(&mut self, callback: Box<InputCallback>)  {
+    pub fn set_input_callback(&mut self, callback: Box<dyn InputCallback>)  {
         self.0.set_input_callback(callback)
     }
 

src/os/unix/mod.rs

@@ -534,7 +534,7 @@ impl Window {
     }
 
     #[inline]
-    pub fn set_input_callback(&mut self, callback: Box<InputCallback>) {
+    pub fn set_input_callback(&mut self, callback: Box<dyn InputCallback>) {
         self.key_handler.set_input_callback(callback)
     }