service:check --markdown or --json exits 0 on breaking changes

**Intended outcome:** When running service:check and the schema has breaking changes, the program should always exit with the same non-zero exit code, regardless of output formatter

**Actual outcome:** When running `service:check --json` or `service:check --markdown` with a breaking change schema, got an exit value of 0

**How to reproduce the issue:** Create a breaking change for a schema and then run `service:check --markdown`

**Versions** `apollo/2.21.1 linux-x64 node-v10.13.0`

Start at the service:check CLI entry point and reproduce the issue with a schema containing a breaking change, using both --markdown and --json on the reported Apollo CLI version. Trace how each formatter determines the process exit status; done means both formats return the same non-zero status for breaking changes while preserving their output.

Written by the indexing model from the issue text.