Added lint check to not support http://osvdb.org in main url:` field (#639)

Author: jasnow

spec/advisory_example.rb

@@ -94,6 +94,7 @@
       subject { advisory['url'] }
 
       it { expect(subject).to be_kind_of(String) }
+      it { expect(subject).to_not match(%r{\Ahttp(s)?://osvdb\.org}) }
       it { expect(subject).not_to be_empty }
     end