patch 8.1.1619: tests are not run with GUI on Travis

Problem:    Tests are not run with GUI on Travis.
Solution:   Add a testgui job. (Ozaki Kiichi, closes #4609)
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index 7f90b03..184e1a4 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -399,7 +399,7 @@
 endfunc
 
 func Test_error_in_map_expr()
-  if !has('terminal') || (has('win32') && has('gui_running'))
+  if !has('terminal') || has('gui_running')
     throw 'Skipped: cannot run Vim in a terminal window'
   endif