Change default replica port from 9000 to current-dfx-default 8000

[gobengo]

Motivation:

• Use the same port as the default project from dfx new so this project is not too surprising, feels familiar for new devs to learn default conventions.

Elsewhere:

• https://dfinity.atlassian.net/browse/CAN-127

[gobengo]

(reset was in order to re-make commits with gpg signatures (ty https://superuser.com/a/1123928)