Fix type for Data(base64Encoded:options) (#433)

diff --git a/Foundation/Data.swift b/Foundation/Data.swift
index 73d30e4..3e0b853 100644
--- a/Foundation/Data.swift
+++ b/Foundation/Data.swift
@@ -255,8 +255,8 @@
     ///
     /// Returns nil when the input is not recognized as valid Base-64.
     /// - parameter base64String: The string to parse.
-    /// - parameter options: Encoding options. Default value is `[]`.
-    public init?(base64Encoded base64String: String, options: Data.Base64EncodingOptions = []) {
+    /// - parameter options: Decoding options. Default value is `[]`.
+    public init?(base64Encoded base64String: String, options: Data.Base64DecodingOptions = []) {
         if let d = NSData(base64Encoded: base64String, options: Base64DecodingOptions(rawValue: options.rawValue)) {
             _wrapped = _SwiftNSData(immutableObject: d)
         } else {