Update utf16.dart (#33)

Fix Utf6 typo
diff --git a/lib/src/utf16.dart b/lib/src/utf16.dart
index 5864120..f1b64fa 100644
--- a/lib/src/utf16.dart
+++ b/lib/src/utf16.dart
@@ -9,7 +9,7 @@
 import 'package:ffi/ffi.dart';
 
 /// [Utf16] implements conversion between Dart strings and null-terminated
-/// Utf6-encoded "char*" strings in C.
+/// UTF-16 encoded "char*" strings in C.
 ///
 /// [Utf16] is respresented as a struct so that `Pointer<Utf16>` can be used in
 /// native function signatures.