patch 8.1.1860: map timeout test is flaky

Problem:    Map timeout test is flaky.
Solution:   Add test to list of flaky tests.  Increase timeout.
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index 6b9fb9c..93a4d4b 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -298,7 +298,7 @@
   let g:val = 0
   nnoremap \12 :let g:val = 1<CR>
   nnoremap \123 :let g:val = 2<CR>
-  set timeout timeoutlen=100
+  set timeout timeoutlen=200
 
   func ExitCb(job, status)
     let g:timer = timer_start(1, {-> feedkeys("3\<Esc>", 't')})