set_to_spaces.md

Sublime: Go to Preferences -> Settings -> More -> Syntax Specific -> User. This should open a settings window named Ruby.sublime-settings

{
  "tab_size": 2,
  "translate_tabs_to_spaces": true
  "detect_indentation": false
}

Vim:

In ~/.vimrc

set tabstop=2
set shiftwidth=2
set expandtab

Nano:

In ~/.nanorc

set tabsize 2
set tabstospaces

Textmate: http://superuser.com/questions/416004/how-to-adjust-indentation-in-textmate

Emacs:

In ~/.emacs

(setq default-tab-width 2)
(setq-default indent-tabs-mode nil)

@falonofthetower - thanks, the assignment has been updated!