THRIFT-4902: Swift 4 and 5 compatibility (#1827)

diff --git a/lib/swift/Sources/TMap.swift b/lib/swift/Sources/TMap.swift
index 8980377..dcf1481 100644
--- a/lib/swift/Sources/TMap.swift
+++ b/lib/swift/Sources/TMap.swift
@@ -21,7 +21,7 @@
   public typealias Storage = Dictionary<Key, Value>
   public typealias Element = Storage.Element
   public typealias Index = Storage.Index
-  public typealias IndexDistance = Storage.IndexDistance
+  public typealias IndexDistance = Int
   public typealias Indices = Storage.Indices
   public typealias SubSequence = Storage.SubSequence
   internal var storage = Storage()
@@ -33,11 +33,7 @@
   }
   
   public mutating func updateValue(_ value: Value, forKey key: Key) -> Value? {
-    return updateValue(value, forKey: key)
-  }
-  
-  public mutating func removeAtIndex(_ index: DictionaryIndex<Key, Value>) -> (Key, Value) {
-    return removeAtIndex(index)
+    return storage.updateValue(value, forKey: key)
   }
   
   public mutating func removeValueForKey(_ key: Key) -> Value? {