[ts]Set false to default value of TsTypePredicate.asserts (#12352)

packages/babel-parser/src/plugins/typescript/index.js

@@ -357,6 +357,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       const node: N.TsTypePredicate = this.startNodeAtNode(lhs);
       node.parameterName = lhs;
       node.typeAnnotation = this.tsParseTypeAnnotation(/* eatColon */ false);
+      node.asserts = false;
       return this.finishNode(node, "TSTypePredicate");
     }
 

packages/babel-parser/src/types.js

@@ -1262,7 +1262,7 @@ export type TsTypePredicate = TsTypeBase & {
   type: "TSTypePredicate",
   parameterName: Identifier | TsThisType,
   typeAnnotation: TsTypeAnnotation,
-  asserts?: boolean,
+  asserts: boolean,
 };
 
 // `typeof` operator