Specifying a client in a mutation throws type error

[anonrose]

    await this.$apollo.mutate({
      mutation: MUTATION_CODE,
      variables: {
        ..
      },
      client: "client"
    });```

will throw the following error       

TS2345: Argument of type '{ mutation: any; variables: {  }; client: string; }' is not assignable to parameter of type 'VueApolloMutationOptions<any, any>'.
  Object literal may only specify known properties, and 'client' does not exist in type 'VueApolloMutationOptions<any, any>'.

Resolved this in https://github.com/Akryum/vue-apollo/pull/644

[anonrose]

Resolved this in #644