lb4: fix usage of Context#get to specify type (#637)

Author: bajtos

pages/en/lb4/Context.md

@@ -132,7 +132,7 @@ store along with the key. For example:
 // app level
 const app = new Application();
 app.bind('hello').to('world'); // ContextKey='hello', ContextValue='world'
-console.log(app.getSync('hello')); // => 'world'
+console.log(app.getSync<string>('hello')); // => 'world'
 ```
 
 In this case, we bind the 'world' string ContextValue to the 'hello' ContextKey.

pages/en/lb4/Decorators.md

@@ -290,7 +290,7 @@ Syntax: `@inject.tag(tag: string | RegExp)`.
     .bind('store.locations.sj')
     .to('San Jose')
     .tag('store:location');
-  const store: Store = ctx.getSync('store');
+  const store = ctx.getSync<Store>('store');
   // `store.locations` is now `['San Francisco', 'San Jose']`
 ```
 
@@ -305,7 +305,7 @@ Syntax: `@inject.context()`.
 
   const ctx = new Context();
   ctx.bind('my-component').toClass(MyComponent);
-  const component: MyComponent = ctx.getSync('my-component');
+  const component = ctx.getSync<MyComponent>('my-component');
   // `component.ctx` should be the same as `ctx`
 ```
 

pages/en/lb4/Extending-LoopBack-4.md

@@ -64,7 +64,7 @@ ctx.bind('utilities.PasswordHash').to((password) => { /* ... */ })
 ctx.bind('controllers.UserController').toClass(UserController);
 
 // Locate the an instance of UserController from the context
-const userController: UserController = await ctx.get('controller.UserController');
+const userController= await ctx.get<UserController>('controller.UserController');
 // Run the log()
 const ok = await logger.login('John', 'MyPassWord');
 ```