Errors on `npm run dev`

[vporton]

Steps to reproduce

master branch (commit commit 8f79ef4294d3e8623bd1ebbdab7fbeb766b29957).

$ nvm use
...
$ npm install
...
nvm run dev
...
Starting db...

> colonyServer@1.6.0 db:start
> ts-node scripts/db-start.ts

/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:423
    return new TSError(diagnosticText, diagnosticCodes)
           ^
TSError: ⨯ Unable to compile TypeScript:
scripts/db-start.ts(1,35): error TS2307: Cannot find module 'mongodb-memory-server'.

    at createTSError (/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:423:12)
    at reportTSError (/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:427:19)
    at getOutput (/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:554:36)
    at Object.compile (/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:760:32)
    at Module.m._compile (/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:839:43)
    at Module._extensions..js (internal/modules/cjs/loader.js:1114:10)
    at Object.require.extensions.<computed> [as .ts] (/home/porton/Projects/colonyDapp/node_modules/ts-node/src/index.ts:842:12)
    at Module.load (internal/modules/cjs/loader.js:950:32)
    at Function.Module._load (internal/modules/cjs/loader.js:790:12)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:76:12)

Expected behaviour

Start.

Actual behaviour

Error message.