build(flow): include node_modules in flow config

[mrfelton]

Problem / Motivation

We're missing flow type definitions for grpc. This is due to the fact that it is installed in app/node_modules and not node_modules

$ yarn flow
yarn run v1.9.2
$ flow
Launching Flow server for /Users/tom/workspace/zap-desktop
Spawned flow server (pid=76836)
Logs will go to /private/tmp/flow/zSUserszStomzSworkspacezSzZap-desktop.log
Monitor logs will go to /private/tmp/flow/zSUserszStomzSworkspacezSzZap-desktop.monitor_log
Error ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ app/lib/lnd/lightning.js:3:18

Cannot resolve module grpc.

     1│ // @flow
     2│
     3│ import grpc from 'grpc'
     4│ import { loadSync } from '@grpc/proto-loader'
     5│ import { BrowserWindow } from 'electron'
     6│ import LndConfig from './config'

Proposed Solution

Currently, in our .flowconfig file we specifically exclude node_modules and app/node_modules. I believe that this is left over from electron-react-boilerplate and it isn't needed.

See facebook/flow#869 for some context about why node_modules shouldn't really be excluded.

This PR adds node_modules and app/node_modules back into the flow type processing, which as well as fixing the above issue, also makes flow generally more useful as it will provide type hints for many more packages.

[coveralls]

Pull Request Test Coverage Report for Build 3796

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 12.696%

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Totals
Change from base Build 3793:	0.0%
Covered Lines:	485
Relevant Lines:	3350

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💛 - Coveralls

[JimmyMow]

Concept ACK 8c5f2bb