Add DuplicateResourceError

Author: javierjulio

lib/dwolla_v2/errors/duplicate_resource_error.rb

@@ -0,0 +1,4 @@
+module DwollaV2
+  class DuplicateResourceError < Error
+  end
+end

spec/dwolla_v2/error_spec.rb

@@ -242,6 +242,14 @@
     }
   end
 
+  it ".raise! code: DuplicateResource" do
+    expect {
+      DwollaV2::Error.raise! code: "DuplicateResource"
+    }.to raise_error {|e|
+      expect(e).to be_a DwollaV2::DuplicateResourceError
+    }
+  end
+  
   it ".raise! Struct(status, headers, body)" do
     status = 400
     headers = { foo: "bar" }