Combine two arrays of hashes

arrays.rb

a = [
  { key: "key1", value: "value1" },
  { key: "key2", value: "value2" }
]
b = [
  { key: "key3", value: "value3" },
  { key: "key4", value: "value4" }
]

a.push(b)

### Output
[{:key=>"key1", :value=>"value1"}, {:key=>"key2", :value=>"value2"}, [{:key=>"key3", :value=>"value3"}, {:key=>"key4", :value=>"value4"}]]

### What I need (no nested arrays)
[{:key=>"key1", :value=>"value1"}, {:key=>"key2", :value=>"value2"}, {:key=>"key3", :value=>"value3"}, {:key=>"key4", :value=>"value4"}]