Remove redundant recommended OSX tool 'autojump' 

autojump 'j' functionality is matched/replaced by fasd 'z' command (installed and enabled as a prezto submodule by default). Instead of typing `j [dirspec]`, you simply type `z [dirspec]`.
Merge pull request #377 from phillipalexander/patch-1

Remove redundant recommended OSX tool 'autojump'  from README.md