Fix #pluck method behavior when 3+ attributes specified

lib/active_hash/relation.rb

@@ -73,7 +73,16 @@ def size
     end
 
     def pluck(*column_names)
-      column_names.map { |column_name| all.map(&column_name.to_sym) }.inject(&:zip)
+      symbolized_column_names = column_names.map(&:to_sym)
+
+      if symbolized_column_names.length == 1
+        column_name = symbolized_column_names.first
+        all.map { |record| record[column_name] }
+      else
+        all.map do |record|
+          symbolized_column_names.map { |column_name| record[column_name] }
+        end
+      end
     end
 
     def ids

spec/active_hash/base_spec.rb

@@ -527,17 +527,22 @@ class Region < ActiveHash::Base
   describe ".pluck" do
     before do
       Country.data = [
-        {:id => 1, :name => "US"},
-        {:id => 2, :name => "Canada"}
+        {:id => 1, :name => "US", :language => "English"},
+        {:id => 2, :name => "Canada", :language => "English"},
+        {:id => 3, :name => "Mexico", :language => "Spanish"}
       ]
     end
 
-    it "returns an two dimensional Array of attributes values" do
-      expect(Country.pluck(:id, :name)).to match_array([[1,"US"], [2, "Canada"]])
+    it "returns an two dimensional Array of 3 attributes values" do
+      expect(Country.pluck(:id, :name, :language)).to match_array([[1, "US", "English"], [2, "Canada", "English"], [3, "Mexico", "Spanish"]])
+    end
+
+    it "returns an two dimensional Array of 2 attributes values" do
+      expect(Country.pluck(:id, :name)).to match_array([[1, "US"], [2, "Canada"], [3, "Mexico"]])
     end
 
     it "returns an Array of attribute values" do
-      expect(Country.pluck(:id)).to match_array([1,2])
+      expect(Country.pluck(:id)).to match_array([1, 2, 3])
     end
   end