Updates outdated dependecies

Use https://rubygems.org as gems source …
To get rid of the following deprecation warning:
```
The source :rubygems is deprecated because HTTP requests are insecure.
Please change your source to 'https://rubygems.org'; if possible, or 'http://rubygems.org'; if not.
```

Bump RSpec version and add rspec-its …
RSpec needed to be upgraded to void getting this error when installing the dependencies:
```
An error occurred while installing rspec-expectations (2.7.0), and Bundler cannot continue.
Make sure that `gem install rspec-expectations -v '2.7.0'` succeeds before bundling.
```
Adding rspec-it was necessary since rpsec -v2.99.0 extracted `its {}` type of assertion in the process of migrating to Rspec 3.

Convert specs to RSpec 2.99.1 syntax. Gets rid of every deprecation warning.