Merge branch 'master' of https://gitlab.zalopay.vn/zalopay-oss/advanc…

…ed-go-book

update gitbook

Merge branch 'dev' into 'master'

#Refactor chapters 4, 5, 6 and change position chapters

See merge request zalopay-oss/advanced-go-book!89

update chap02

Refactor chapter 1

Merge branch 'dev' into 'master'

Merge branch 'dev' into 'master'

See merge request zalopay-oss/advanced-go-book!42