Bump lastUpgradeCheck to Xcode 9.4.

This should prevent the `Update to recommended settings` warnings when
using Xcode 9.4 and below.

PiperOrigin-RevId: 204973286
diff --git a/src/TulsiGenerator/PBXObjects.swift b/src/TulsiGenerator/PBXObjects.swift
index c989c32..1c202e9 100644
--- a/src/TulsiGenerator/PBXObjects.swift
+++ b/src/TulsiGenerator/PBXObjects.swift
@@ -1111,7 +1111,7 @@
   }
 
   let compatibilityVersion = XcodeVersionInfo.compatibilityVersion
-  let lastUpgradeCheck = "0900"
+  let lastUpgradeCheck = "0940"
   /// May be set to an Xcode version string indicating the last time a Swift upgrade check was
   /// performed (e.g., 0710).
   var lastSwiftUpdateCheck: String? = nil