Can't start the MongoDB

[vporton]

Steps to reproduce

The bug appears in commit ae76c496.

$ npm run dev
...
> colonyServer@1.6.0 db:start
> ts-node scripts/db-start.ts

(node:3971239) UnhandledPromiseRejectionWarning: Error: Incorrect State for operation: "new", allowed States: "[running,starting]"
This may be because of using a v6.x way of calling functions, look at the following guide if anything applies:
https://nodkz.github.io/mongodb-memory-server/docs/guides/migration/migrate7#no-function-other-than-start-create-ensureinstance-will-be-starting-anything
    at MongoMemoryServer.getUri (/home/porton/Projects/colonyDapp/node_modules/mongodb-memory-server-core/src/MongoMemoryServer.ts:727:15)
    at /home/porton/Projects/colonyDapp/src/lib/colonyServer/scripts/db-start.ts:18:28
    at Generator.next (<anonymous>)
    at /home/porton/Projects/colonyDapp/src/lib/colonyServer/scripts/db-start.ts:8:71
    at new Promise (<anonymous>)
    at __awaiter (/home/porton/Projects/colonyDapp/src/lib/colonyServer/scripts/db-start.ts:4:12)
    at startMongod (/home/porton/Projects/colonyDapp/src/lib/colonyServer/scripts/db-start.ts:8:32)
    at Object.<anonymous> (/home/porton/Projects/colonyDapp/src/lib/colonyServer/scripts/db-start.ts:22:1)
    at Module._compile (internal/modules/cjs/loader.js:1085:14)
    at Module.m._compile (/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:839:23)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:3971239) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:3971239) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Here the process is stalled.