Comment typo fix in es2015.ts: "propety"

src/compiler/transformers/es2015.ts

@@ -2553,7 +2553,7 @@ namespace ts {
         }
 
         /**
-         * Visits an ObjectLiteralExpression with computed propety names.
+         * Visits an ObjectLiteralExpression with computed property names.
          *
          * @param node An ObjectLiteralExpression node.
          */