fix(component): remove ? from LetViewContext props to prevent 'possib…

…ly undefined' error in strict mode

modules/component/src/let/let.directive.ts

@@ -15,13 +15,13 @@ import { createRender } from '../core/cd-aware/creator_render';
 
 export interface LetViewContext<T> {
  // to enable `let` syntax we have to use $implicit (var; let v = var)
- $implicit?: T;
+ $implicit: T;
  // to enable `as` syntax we have to assign the directives selector (var as v)
- ngrxLet?: T;
+ ngrxLet: T;
  // set context var complete to true (var$; let e = $error)
- $error?: boolean;
+ $error: boolean;
  // set context var complete to true (var$; let c = $complete)
- $complete?: boolean;
+ $complete: boolean;
 }
 
 /**