patch 8.1.1614: 'numberwidth' can only go up to 10

Problem:    'numberwidth' can only go up to 10.
Solution:   Allow up to 20. (Charlie Stanton, closes #4584)
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index e8eaef0..cbe0084 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -245,7 +245,7 @@
   call assert_fails('set backupcopy=', 'E474:')
   call assert_fails('set regexpengine=3', 'E474:')
   call assert_fails('set history=10001', 'E474:')
-  call assert_fails('set numberwidth=11', 'E474:')
+  call assert_fails('set numberwidth=21', 'E474:')
   call assert_fails('set colorcolumn=-a')
   call assert_fails('set colorcolumn=a')
   call assert_fails('set colorcolumn=1,')