client:download-schema produces error when run in gitlab CI

**Intended outcome:**
Apollo CLI successfully generates a `schema.json` with the `apollo client:download-schema` command while run in gitlab CI.

The gitlab-ci.yml instructions:

```
create:schema:
stage: package
before_script:
- cd schema_gql
- npm install
- nohup npm run start:ci &
script:
# - trap 'kill $(jobs -p)' EXIT
- sleep 10
- npm run schema:download
- cat ./publish/lon-homeppl-v0-0-1.graphql
- echo created schema ready to deploy
- exit
```

The `schema:download` script: `npx apollo client:download-schema ./publish/lon-homeppl-v0-0-1.graphql --endpoint http://localhost:4000/graphql --tagName current`

the script works fine when run locally and when the gitlab ci is run locally. It only fails during CI.

**Actual outcome:**
The download fails with the following output:
```
A config file failed to load with options: {"type":"client"}.
The error was: Error: Cannot find module 'dotenv'
at Object.loadConfig (/builds/homeppl/wizard/schema_gql/node_modules/apollo-language-server/lib/config/loadConfig.js:39:34)
› Error: A config failed to load, so the command couldn't be run
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! schema_gql@1.0.0 schema:download: `npx apollo client:download-schema ./publish/lon-homeppl-v0-0-1.graphql --endpoint http://localhost:4000/graphql --tagName current`
npm ERR! Exit status 2
npm ERR!
npm ERR! Failed at the schema_gql@1.0.0 schema:download script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /root/.npm/_logs/2019-12-02T15_02_17_947Z-debug.log
```
I've checked the `apollo-language-server` file mentioned above an nowhere does it mention `dotenv`. I even tried installing it as a dep but no luck.

**How to reproduce the issue:**

**Versions**
`apollo`: `^2.21.1`

Reproduce the `apollo client:download-schema` command from the provided GitLab CI steps, starting with the config-loading failure in `apollo-language-server/lib/config/loadConfig.js`. Compare the local and CI dependency/config environments, then verify that the command creates the requested schema file in GitLab CI without the `dotenv` error.

Written by the indexing model from the issue text.