fix core import

tanner0101 · tanner0101 · commit 387cf9ea6e90 · 2018-03-22T15:11:23.000-04:00
diff --git a/Sources/PostgreSQL/Data/PostgreSQLData+Optional.swift b/Sources/PostgreSQL/Data/PostgreSQLData+Optional.swift
@@ -1,5 +1,5 @@
 import Async
-import Foundation
+import Core
 
 extension OptionalType {
     /// See `PostgreSQLDataCustomConvertible.convertFromPostgreSQLData(_:)`
