Add ts2.8 tag

index.ts

@@ -9,6 +9,7 @@ Example:
 // TypeScript Version: 2.1
 */
 
+/** Parse-able TypeScript versions. Only add to this list if we will support this version on DefinitelyTyped. */
 export type TypeScriptVersion = "2.0" | "2.1" | "2.2" | "2.3" | "2.4" | "2.5" | "2.6";
 export namespace TypeScriptVersion {
 	export const all: ReadonlyArray<TypeScriptVersion> = ["2.0", "2.1", "2.2", "2.3", "2.4", "2.5", "2.6"];
@@ -34,6 +35,7 @@ export namespace TypeScriptVersion {
 		"ts2.5",
 		"ts2.6",
 		"ts2.7",
+		"ts2.8",
 		"latest",
 	];