Resolves #38 - always set autoindent

[SidOfc]

This small patch fixes #38.

Vim does not have autoindent enabled by default, from :h autoindent:

			*'autoindent'* *'ai'* *'noautoindent'* *'noai'*
'autoindent' 'ai'	boolean	(default off)

The same documentation in Nvim :h autoindent:

			*'autoindent'* *'ai'* *'noautoindent'* *'noai'*
'autoindent' 'ai'	boolean	(default on)

The tests kept working because they assumed &formatoptions to be 1 by setting it before the tests and restoring it afterwards.