bug: No longer able to start server

[ermshiperete]

The server now requires a private key in order to start so that the keymanapp-test-bot is able to run.

It should either be documented how such a private key can be acquired, or the code changed to ignore the test-bot if the private
key can't be found.

npm run start-server outputs:

10:39:33 AM - Found 0 errors. Watching for file changes.
Error: [@octokit/auth-app] privateKey option is required
    at Object.createAppAuth (.../status.keyman.com/server/node_modules/@octokit/auth-app/dist-src/index.js:14:15)
    at getState (.../status.keyman.com/server/node_modules/octokit-auth-probot/dist-src/get-state.js:19:19)
    at authStrategy (.../status.keyman.com/server/node_modules/octokit-auth-probot/dist-src/index.js:5:19)
    at new Octokit (.../status.keyman.com/server/node_modules/@octokit/core/dist-src/index.js:69:26)
    at new _a (.../status.keyman.com/server/node_modules/@octokit/core/dist-src/index.js:117:34)
    at new OctokitWithDefaults (.../status.keyman.com/server/node_modules/@octokit/core/dist-src/index.js:96:21)
    at new OctokitWithDefaults (.../status.keyman.com/server/node_modules/@octokit/core/dist-src/index.js:96:21)
    at new Probot (.../status.keyman.com/server/node_modules/probot/src/probot.ts:74:21)
    at Object.<anonymous> (.../status.keyman.com/server/keymanapp-test-bot/keymanapp-test-bot-middleware.ts:35:16)
    at Module._compile (internal/modules/cjs/loader.js:1158:30)