Fixed regex of `NERDTreeIgnore`.

NERDTree does'nt show directory which name containing '.git' '.svn' or '.hg'(e.g. 'cupen.github', 'a.svna').
The regx of `NERDTreeIgnore` was‘nt working right,I fixed it..
Ensure HOME environmental variable set

When working with puppet (and other setups), it is possible the HOME environmental variable is unset. This
leads to a spf13 bootstrap which does not perform as expected because `$HOME` is empty. This results in files being written to undesirable locations such as `/.spf13-vim-3/.vimrc.bundles` Let's stop the user before they get into this bad state.
Add support for Salt files
Adopting the Apache 2 License. Fixed #653
change airline theme