Update SWIFT_VERSION to 4.2 in .xcconfig

Base32.xcodeproj/Configs/Project.xcconfig

@@ -35,4 +35,4 @@ GCC_WARN_UNDECLARED_SELECTOR = YES;
 GCC_WARN_UNINITIALIZED_AUTOS = YES;
 GCC_WARN_UNUSED_FUNCTION = YES;
 GCC_WARN_UNUSED_VARIABLE = YES;
-SWIFT_VERSION = 4.0;
+SWIFT_VERSION = 4.2;