fix: dotenv/main debug option not work

[189]

fix the issue 548
All those will active debug mode:

  dotenv.config({ debug: true })
  dotenv.config({ debug: 1 })
  dotenv.config({ debug: 'some string' })

And belows will not:

  dotenv.config({ debug: false })
  dotenv.config({ debug: null })
  dotenv.config({ })
  dotenv.config({ debug: 0 })

[bigmeow]

I think this code change is better than your`s

  let dotenvPath = path.resolve(process.cwd(), '.env')
  let encoding /*: string */ = 'utf8'
  const debug = Boolean(options && options.debug)

  if (options) {
    if (options.path != null) {
      dotenvPath = resolveHome(options.path)
    }
    if (options.encoding != null) {
      encoding = options.encoding
    }
  }

[motdotla]

Thank you for this. I will additionally modify to @bigmeow's recommendation after merging.