fix typo 2

Author: GarmashAlex

src/musig.rs

@@ -1034,7 +1034,7 @@ impl AggregatedSignature {
     }
 }
 
-/// A musig Siging session.
+/// A musig Signing session.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Session(ffi::MusigSession);