Update README.md

$ git clone git@github.com:ntaoo/tiny-ruby-snippet.git
Cloning into 'tiny-ruby-snippet'...
Permission denied (publickey).
fatal: Could not read from remote repository.

$ git clone git://github.com/ntaoo/tiny-ruby-snippet.git
Cloning into 'tiny-ruby-snippet'...
remote: Counting objects: 14, done.
remote: Compressing objects: 100% (11/11), done.
remote: Total 14 (delta 3), reused 10 (delta 2)
Receiving objects: 100% (14/14), done.
Resolving deltas: 100% (3/3), done.
Merge pull request #1 from kusanaginoturugi/master

git clone の URLがおかしいようなので修正しました。