Merge pull request #2371 from vim-airline/add_commands_test_case

[add] AirlineExtensions's test case

t/commands.vim

@@ -31,4 +31,9 @@ describe 'commands'
   it 'should have a refresh command'
     Expect exists(':AirlineRefresh') to_be_true
   end
+
+  it 'should have a extensions command'
+    Expect exists(':AirlineExtensions') to_be_true
+  end
+
 end