Vim error

To clarify #592, I would add something:

* `set background=dark/light` works when you start vim and input the command, but when it's in `.vimrc`, it won't work even inputting the command after starting. Error message when starting:
```
Error detected while processing /private/var/mobile/Containers/Data/Applicatio
n/0DBB0FAE-99DD-46AE-AD6A-A647C60C47B7/Documents/.vimrc:
line 3:
E518: Unknown option: light
```
And when inputting the command it just did nothing.
* `set colorscheme balabala` works when reading `.vimrc`, but without `set background` working, it looks ugly as #592. When run the command without reading `.vimrc`, it returns:
```
E518: Unknown option: colorscheme
```
Hope info above help reproduce the problem.