Update doc/api/buffer.md

Co-authored-by: James M Snell <[email protected]>

Author: benjamingr

doc/api/buffer.md

@@ -3391,7 +3391,7 @@ added: v0.3.0
 changes:
   - version: REPLACEME
     pr-url: https://github.com/nodejs/node/pull/41596
-    description: The buf.slice method has been deprecated.
+    description: The buf.slice() method has been deprecated.
   - version:
     - v7.1.0
     - v6.9.2