Use DefaultHasher in place of the deprecated SipHasher

src/key.rs

@@ -673,11 +673,12 @@ mod test {
 
     #[test]
     fn pubkey_hash() {
-        use std::hash::{Hash, SipHasher, Hasher};
+        use std::collections::hash_map::DefaultHasher;
+        use std::hash::{Hash, Hasher};
         use std::collections::HashSet;
 
         fn hash<T: Hash>(t: &T) -> u64 {
-            let mut s = SipHasher::new();
+            let mut s = DefaultHasher::new();
             t.hash(&mut s);
             s.finish()
         }