Set the ModuleKind value for ESNext to be 99 so it doesn't change between releases (and yet another module system?!)

src/compiler/types.ts

@@ -4760,7 +4760,7 @@ namespace ts {
         UMD = 3,
         System = 4,
         ES2015 = 5,
-        ESNext = 6
+        ESNext = 99
     }
 
     export const enum JsxEmit {