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..
Merge pull request #661 from Cupen/patch-1

Fixed regex of `NERDTreeIgnore`.