Fix: Expose Installments#list instead of #retrieve

Author: wacko

README.md

@@ -76,6 +76,6 @@ This are the operations available for each resource:
 |Cards         | x | x | x | x | x |   |
 |Charges       | x | x | x |   |   |   |
 |Customers     | x | x | x | x | x |   |
-|Installments  |   |   | x |   |   |   |
+|Installments  | x |   |   |   |   |   |
 |Queue         | x | x | x |   | x | x |
 |Refunds       | x | x | x |   |   |   |

lib/mango/resources.rb

@@ -31,7 +31,7 @@ class Queue < Resource
   end
 
   class Installments < Resource
-    public_class_method :retrieve
+    public_class_method :list
   end
 
 end