message: refactor(service:check): Ensure `project` is service project
  We shouldn't be forcing a type cast; we should instead check and guarantee
  the type.
diff: @@ -11,7 +11,11 @@ import {
  ChangeSeverity,
  CheckSchemaVariables
  } from "apollo-language-server/lib/graphqlTypes";
  -import { ApolloConfig, GraphQLServiceProject } from "apollo-language-server";
  +import {
  + ApolloConfig,
  + GraphQLServiceProject,
  + isServiceProject
  +} from "apollo-language-server";
  import moment from "moment";
  import sortBy from "lodash.sortby";
  @@ -258,6 +262,12 @@ export default class ServiceCheck extends ProjectCommand {
  try {
  await this.runTasks<TasksOutput>(
  ({ config, flags, project }) => {
  + if (!isServiceProject(project)) {
  + throw new Error(
  + "This project needs to be configured as a service project but is configured as a client project. Please see bit.ly/2ByILPj for help regarding configuration."
  + );
  + }
  +
  const configName = config.name;
  const tag = flags.tag || config.tag || "current";
  @@ -275,7 +285,7 @@ export default class ServiceCheck extends ProjectCommand {
  taskOutput.shouldOutputJson = flags.json;
  if (flags.federated) {
  - const info = await (project as GraphQLServiceProject).resolveFederationInfo();
  + const info = await project.resolveFederationInfo();
  if (!info.sdl)
  throw new Error("No SDL found for federated service");
  