Provide localizedDescription for our errors

Commit minor changes to Social and OMG extensions.

Extensions/OMGHTTPURLRQ

@@ -1 +1 @@
-Subproject commit 97bcc046a9ed782c0493ff7897cdbb6c57979099
+Subproject commit 0d0d5a18021cb007b18a4a96e6cf4163f67f41c7

Extensions/Social

@@ -1 +1 @@
-Subproject commit 04d8d7ad1f3cb0649b4f4f648e73095ab79c7049
+Subproject commit 34cc22feb6738d73b71f6fb532020068df489586

Sources/Error.swift

@@ -23,8 +23,8 @@ public enum PMKError: Error {
     case flatMap(Any, Any.Type)
 }
 
-extension PMKError: CustomStringConvertible {
-    public var description: String {
+extension PMKError: CustomDebugStringConvertible {
+    public var debugDescription: String {
         switch self {
         case .flatMap(let obj, let type):
             return "Could not `flatMap<\(type)>`: \(obj)"
@@ -35,11 +35,17 @@ extension PMKError: CustomStringConvertible {
         case .badInput:
             return "Bad input was provided to a PromiseKit function"
         case .cancelled:
-            return "The operation was cancelled"
+            return "The asynchronous sequence was cancelled"
         }
     }
 }
 
+extension PMKError: LocalizedError {
+    public var errorDescription: String? {
+        return debugDescription
+    }
+}
+
 
 //////////////////////////////////////////////////////////// Cancellation