Add missing hyphen

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/ChangeLog.d/safer-ct.txt b/ChangeLog.d/safer-ct.txt
index 6c417f4..0a5b632 100644
--- a/ChangeLog.d/safer-ct.txt
+++ b/ChangeLog.d/safer-ct.txt
@@ -2,5 +2,5 @@
    * Updates to constant-time C code so that compilers are less likely to use
      conditional instructions, which can have an observable difference in
      timing. (Clang has been seen to do this.) Also introduce assembly
-     implementations for 32 and 64-bit Arm and for x86 and x86-64, which are
+     implementations for 32- and 64-bit Arm and for x86 and x86-64, which are
      guaranteed not to use conditional instructions.