Detects dupe keys on arrays of hashes

[shortdudey123]

The following is a valid YAML file but yamllint detects dupe keys on foo

---
- foo: 1
  bar: 2
- foo: 1
  bar: 2

Loads into Ruby like so:

[{"foo"=>1, "bar"=>2}, {"foo"=>1, "bar"=>2}]

YamlLint output:

$ bundle exec ruby bin/yamllint spec/data/valid2.yaml 
Checking 1 files
spec/data/valid2.yaml
  The same key is defined more than once: 
  The same key is defined more than once: .foo
  The same key is defined more than once: .bar
YAML lint found 1 errors
$