Fix comment (microsoft#24035)

Author: Andy

src/compiler/types.ts

@@ -538,7 +538,7 @@ namespace ts {
 Abstract = 1 << 7, // Class/Method/ConstructSignature
 Async = 1 << 8, // Property/Method/Function
 Default = 1 << 9, // Function/Class (export default declaration)
-Const = 1 << 11, // Variable declaration
+Const = 1 << 11, // Const enum
 HasComputedFlags = 1 << 29, // Modifier flags have been computed
 
 AccessibilityModifier = Public | Private | Protected,