[interpreter] Fix typo in comment (#1045)

diff --git a/interpreter/binary/utf8.mli b/interpreter/binary/utf8.mli
index 3a70c3c..3b5994a 100644
--- a/interpreter/binary/utf8.mli
+++ b/interpreter/binary/utf8.mli
@@ -1,4 +1,4 @@
 exception Utf8
 
-val decode : string -> int list (* raises UTf8 *)
+val decode : string -> int list (* raises Utf8 *)
 val encode : int list -> string (* raises Utf8 *)