fix(types): The typings for DollarApollo where missing getClient (#727)

* fix(types): add getClient to DollarApollo

* Add documentation for `DollarApollo.getClient`

Author: M-Zuber

docs/api/dollar-apollo.md

@@ -19,4 +19,5 @@ This is the Apollo manager added to any component that uses Apollo. It can be ac
 - `mutate`: execute a mutation (see [Mutations](../guide/apollo/mutations.md)).
 - `subscribe`: standard Apollo subscribe method (see [Subscriptions](../guide/apollo/subscriptions.md)).
 - `addSmartQuery`: manually add a Smart Query (not recommended).
-- `addSmartSubscription`: add a Smart Subscription (see [Subscriptions](../guide/apollo/subscriptions.md)).
+- `addSmartSubscription`: add a Smart Subscription (see [Subscriptions](../guide/apollo/subscriptions.md)).
+- `getClient`: returns the underlying ApolloClient.

types/vue-apollo.d.ts

@@ -53,6 +53,7 @@ export interface DollarApollo<V> {
   /* writeonly */ skipAllSubscriptions: boolean;
   /* writeonly */ skipAll: boolean;
 
+  getClient<R=any>(): ApolloClient<R>;
   query<R=any>(options: VueApolloQueryOptions<V, R>): Promise<ApolloQueryResult<R>>;
   mutate<R=any>(options: VueApolloMutationOptions<V, R>): Promise<FetchResult<R>>;
   subscribe<R=any>(options: VueApolloSubscriptionOptions<V, R>): Observable<FetchResult<R>>;
@@ -61,4 +62,4 @@ export interface DollarApollo<V> {
   addSmartSubscription<R=any>(key: string, options: VueApolloSubscriptionOptions<V, R>): SmartSubscription<V>;
 }
 
-export function willPrefetch (component: VueApolloComponent, contextCallback?: boolean): VueApolloComponent
+export function willPrefetch (component: VueApolloComponent, contextCallback?: boolean): VueApolloComponent