Adds flag to give back SSH url instead of HTTP

@supremebeing7 I am finding that this fails for me.

`githubrepo repo_name -s`
Here we've said that we want the ssh url. However, there is no where in the code that actually sets the variable `ssh`. See line 31.

I really could be mistaken, this is the error I get.
`error: undefined local variable or method `ssh' for main:Object. Use --trace to view backtrace`

Error with backtrace
`./bin/githubrepo:51:in `block (2 levels) in <main>': undefined local variable or method `ssh' for main:Object (NameError)`

I'll go ahead and make sure `:wants_ssh` receives a value from the command line flag. I expect the value being received to be true.