docs(toh-4): change var keyword to const for HEROES constant closes #1858 HEROES is a `const` and is defined as a `const` originally: https://github.com/angular/angular.io/blob/master/public/docs/_examples/toh-2/ts/app/app.component.ts#L10
docs(toh-4): change var keyword to const for HEROES constant
closes #1858
HEROES is a `const` and is defined as a `const` originally: https://github.com/angular/angular.io/blob/master/public/docs/_examples/toh-2/ts/app/app.component.ts#L10

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