docs: fix a few simple typos

[koalalorenzo]

There are small typos in:

• README.md
• digitalocean/Domain.py
• digitalocean/LoadBalancer.py
• digitalocean/VPC.py

Fixes:

• Should read domain rather than doamin.
• Should read boolean rather than boolen.
• Should read attributes rather than attributues.
• Should read advantage rather than advandtage.

Closes #339