Merge pull request #93 from tomburns/swift-3-1-warnings

Silence optional debug print warning in swift 3.1

Author: shams-ahmed

Sources/DataSources/Differentiator.swift

@@ -74,7 +74,7 @@ fileprivate struct SectionAssociatedData {
 extension SectionAssociatedData : CustomDebugStringConvertible {
     fileprivate var debugDescription: String {
         get {
-            return "\(event), \(indexAfterDelete)"
+            return "\(event), \(String(describing: indexAfterDelete))"
         }
     }
 }
@@ -94,7 +94,7 @@ fileprivate struct ItemAssociatedData {
 extension ItemAssociatedData : CustomDebugStringConvertible {
     fileprivate var debugDescription: String {
         get {
-            return "\(event) \(indexAfterDelete)"
+            return "\(event) \(String(describing: indexAfterDelete))"
         }
     }
 }