commit: fix const declaration

commit functions should take an array of const pointers, not a const
array.

examples/merge.c

@@ -263,7 +263,7 @@ static int create_merge_commit(git_repository *repo, git_index *index, struct me
 	                        sign, sign,
 	                        NULL, msg,
 	                        tree,
-	                        opts->annotated_count + 1, (const git_commit **)parents);
+	                        opts->annotated_count + 1, parents);
 	check_lg2(err, "failed to create commit", NULL);
 
 	/* We're done merging, cleanup the repository state */