Upgrade vim-vspec to 1.8.1 (#862)

This fixes some tests to make it work with the newer version.

test/completions.vim

@@ -63,9 +63,6 @@ describe 'completions'
         Expect getline('.') == 'raise BaseException'
         set completeopt +=longest
     end
-
-    it 'dot_open'
-    end
 end
 
 " vim: et:ts=4:sw=4