Fix warnings, remove an unneeded lifetime parameter

Author: pimeys

examples/simple_sender.rs

@@ -33,7 +33,7 @@ fn main() {
     };
 
     let mut builder = MessageBuilder::new(api_key.as_ref(), device_token.as_ref());
-    builder.data(&data);
+    builder.data(&data).unwrap();
 
     let work = client.send(builder.finalize());
 

src/message/mod.rs

@@ -183,7 +183,7 @@ impl MessageBuilder {
     /// builder.data(&map);
     /// let message = builder.finalize();
     /// ```
-    pub fn data<'a>(&mut self, data: &Serialize) -> Result<&mut MessageBuilder, serde_json::Error> {
+    pub fn data(&mut self, data: &Serialize) -> Result<&mut MessageBuilder, serde_json::Error> {
         self.data = Some(serde_json::to_value(data)?);
         Ok(self)
     }

src/message/tests.rs

@@ -1,6 +1,5 @@
 use {MessageBuilder, Priority};
 use notification::NotificationBuilder;
-use std::collections::HashMap;
 use serde_json;
 
 #[test]