Fix tracking issues with #131

[jschwindt]

Hi,

I started using page.tracked?, page.untracked_url and page.untrack! and all three fail with URLs that don't have query values, for example:

page = MetaInspector.new('http://example.com/foo')
page.tracked?
NoMethodError: undefined method `keys' for nil:NilClass
    from /usr/local/var/rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/metainspector-4.6.1/lib/meta_inspector/url.rb:34:in `tracked?'

At the same time, if the URL has only tracking query values, the untracked_url method returns the URL with the question mark (?) at the end:

page = MetaInspector.new('http://example.com/foo?utm_source=twitter')
page.untracked_url
=> "http://example.com/foo?"

I created the missing tests that reproduced those errors and fixed the API.

Hope it helps.

Juan.

[jaimeiniesta]

👍 thanks!