Fix "rails server" command on windows

Hello!
I fixed some commands on Windows in "Rails Girls App Tutorial"(http://guides.railsgirls.com/app/ ) with the first commit.
Then, they are the same as ones on the other environments, so I unified each commands with the second commit.

I checked commands on Windows in the tutorial page with this environments:

<pre>
OS: Windows7 (64bit)

C:\Users\yoiz\Desktop\rails-test\demo>ruby -v
ruby 1.9.3p392 (2013-02-22) [i386-mingw32]

C:\Users\yoiz\Desktop\rails-test\demo>gem -v
1.8.24

C:\Users\yoiz\Desktop\rails-test\demo>rails -v
Rails 3.2.13
</pre>

Thanks.