Fix message when `order` was an invalid value

The symbol that can be used is `:bottom`, not `:down`.
Ref: https://github.com/ruby/ruby/blob/e39b2cff8ac2dc93b35bd43ffcce3ded8e3b4c25/error.c#L1061

[Fix GH-1916]

From: yuuji.yaginuma <yuuji.yaginuma@gmail.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63984 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 1 deletions

diff --git a/error.c b/error.c
index 1deb53af0a..2912f1f7be 100644
--- a/error.c
+++ b/error.c
@@ -1061,7 +1061,7 @@ exc_full_message(int argc, VALUE *argv, VALUE exc)
 	    if (id == id_bottom) args[kw_order] = Qtrue;
 	    else if (id == id_top) args[kw_order] = Qfalse;
 	    else {
-		rb_raise(rb_eArgError, "expected :top or :down as "
+		rb_raise(rb_eArgError, "expected :top or :bottom as "
 			 "order: %+"PRIsVALUE, args[kw_order]);
 	    }
 	}