message: docs(core): add missing quote in dependency injection provider guide
  Add closing double quote in HTML `class` attribute in dependency
  injection provider guide.
  Fixes
  PR Close
diff: @@ -278,7 +278,7 @@ When you provide multiple sets of routes using [RouterModule.forRoot](api/router
  and [RouterModule.forChild](api/router/RouterModule#forchild) in a single module,
  the [ROUTES](api/router/ROUTES) token combines all the different provided sets of routes into a single value.
  -<div class="alert is-helpful>
  +<div class="alert is-helpful">
  Search for [Constants in API documentation](api?type=const) to find more built-in tokens.
  