Add fixes to automate-tests-with-guard.md

Hi, 
I ran into some problems when following the tutorial "Automate Tests with Guard":

4) `bundle exec guard init spec`

My notes: When I ran Item 4, I got ERROR - Could not load 'guard/spec' or '~/.guard/templates/spec' or find class Guard::Spec. I was able to get past this step by running `guard init spec`


5) Edit the Guardfile to add:
    require 'active_support/core_ext'
    guard 'spec, :all_after_pass => false do

My notes: Item 5 seems to be an incomplete code fragment. I ran into errors when I added this to Guardfile.
I skipped this step and ran `bundle exec guard` without any problems.

I rewrote the file to modify step 4, delete step 5 and add step 6 (exiting Guard; Ctrl-C does not seem to do the trick).

Below are the references I used:
https://github.com/guard/guard
https://github.com/guard/guard-rspec

Thanks,
Beth