Fix TS Official Docs Link about Discriminated Unions

ryota-murakami · web-flow · commit f620b3d8d16f · 2020-01-25T23:15:23.000+09:00
Original url is missing `#discriminated-unions` hash fragment identifier end of string.
So our browser can't reach **Discriminated Unions** section in the **Advanced Types** page.
diff --git a/README.md b/README.md
@@ -1145,7 +1145,7 @@ function isAdmin(user: Admin | User): user is Admin {
 
 Method 2 is also known as [User-Defined Type Guards](https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards) and can be really handy for readable code. This is how TS itself refines types with `typeof` and `instanceof`.
 
-If you need `if...else` chains or the `switch` statement instead, it should "just work", but look up [Discriminated Unions](https://www.typescriptlang.org/docs/handbook/advanced-types.html) if you need help. (See also: [Basarat's writeup](https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html)). This is handy in typing reducers for `useReducer` or Redux.
+If you need `if...else` chains or the `switch` statement instead, it should "just work", but look up [Discriminated Unions](https://www.typescriptlang.org/docs/handbook/advanced-types.html#discriminated-unions) if you need help. (See also: [Basarat's writeup](https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html)). This is handy in typing reducers for `useReducer` or Redux.
 
 ## Optional Types
 
