replace usage of deprecated variable. resolves bling#8

Author: bling

vimrc

@@ -659,7 +659,7 @@
         let g:vimshell_editor_command='vim'
       endif
       let g:vimshell_right_prompt='getcwd()'
-      let g:vimshell_temporary_directory='~/.vim/.cache/vimshell'
+      let g:vimshell_data_directory='~/.vim/.cache/vimshell'
       let g:vimshell_vimshrc_path='~/.vim/vimshrc'
 
       nnoremap <leader>c :VimShell -split<cr>