Making Rspec 3 compliant, Fixing deprecation warning #16

Making Rspec 3 compliant fixing the Deprecation warnings 

```
Deprecation Warnings:

--------------------------------------------------------------------------
SunspotMatchers::HaveSearchableField implements a legacy RSpec matcher
protocol. For the current protocol you should expose the failure messages
via the `failure_message` and `failure_message_when_negated` methods.
(Used from /Users/ankitgupta/Documents/projects/work/my-development/spec/models/article_spec.rb:18:in `block (2 levels) in <top (required)>')
--------------------------------------------------------------------------
--------------------------------------------------------------------------
SunspotMatchers::HaveSearchableField implements a legacy RSpec matcher
protocol. For the current protocol you should expose the failure messages
via the `failure_message` and `failure_message_when_negated` methods.
(Used from /Users/ankitgupta/Documents/projects/work/my-development/spec/models/article_spec.rb:19:in `block (2 levels) in <top (required)>')
--------------------------------------------------------------------------


If you need more of the backtrace for any of these deprecations to
identify where to make the necessary changes, you can configure
`config.raise_errors_for_deprecations!`, and it will turn the
deprecation warnings into errors, giving you the full backtrace.

2 deprecation warnings total

Randomized with seed 62963
```