Simplify the cmd/http package overall by removing
custom plain text v/s tls connection detection, by
migrating to go1.12 and choose minimum version
to be go1.12
Also remove all the vendored deps, since they
are not useful anymore.
This PR allows 'minio update' to not only shows update banner
but also allows for in-place upgrades.
Updates are done safely by validating the downloaded
sha256 of the binary.
Fixes#4781
For binary releases and operating systems it would be
All operating systems.
```
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Minio is 25 days 12 hours 30 minutes old ┃
┃ Update: https://dl.minio.io/server/minio/release/linux-amd64/minio ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
```
On docker.
```
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Minio is 25 days 12 hours 32 minutes old ┃
┃ Update: docker pull minio/minio ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
```
