Bump lodash from 4.17.15 to 4.17.20 in /book/2-begin

Bumps [lodash](https://github.com/lodash/lodash) from 4.17.15 to 4.17.20.
- [Release notes](https://github.com/lodash/lodash/releases)
- [Commits](lodash/lodash@4.17.15...4.17.20)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]