Fix collection of strings assuming complex objects. Fixes #30

Author: wjohnstondrip

lib/drip/collection.rb

@@ -24,7 +24,7 @@ def item_class
 
     def parse_items
       raw_items.map do |raw_item|
-        item_class.new(raw_item)
+        raw_item.is_a?(String) ? raw_item : item_class.new(raw_item)
       end
     end
 

test/drip/client/custom_fields_test.rb

@@ -8,7 +8,15 @@ def setup
   context "#custom_fields" do
     setup do
       @response_status = 200
-      @response_body = "{}"
+      @response_body = <<-JSON
+        {
+          "custom_field_identifiers":[
+            "custom_field_1",
+            "custom_field_2",
+            "custom_field_3"
+          ]
+        }
+      JSON
 
       stub_request(:get, "https://api.getdrip.com/v2/12345/custom_field_identifiers").
         to_return(status: @response_status, body: @response_body, headers: {})