ci/compose: add project name using a drone env var

there was an issue where https://git.dotya.ml/dotya.ml/homepage
containers were getting orphaned when this project was deployed.

messages like the following were printed:
Removing orphan container "src_homepage_2"
Removing orphan container "src_homepage_4"
Removing orphan container "src_reverse-proxy_1"
Removing orphan container "src_homepage_3"
Removing orphan container "src_homepage_1"

The author of the accepted answer of a related SO thread links to
docker-compose documentation, explaining how setting a project variable
should resolve this.

the COMPOSE_PROJECT_NAME environment variable is likely the same for
both projects in question here (homepage and docs) as they're both being
deployed by drone from the /drone/src directory, which is also set by
drone as the WORKDIR). basename - here src - is used as the project name
if not specified otherwise.

to conclude, running both [compose deployments] with a unique project
name should fix the issue.

refs:
https://stackoverflow.com/a/59173539
https://docs.docker.com/compose/reference/overview/#use--p-to-specify-a-project-name
https://docs.docker.com/compose/reference/envvars/#compose_project_name

fix #1

.drone.yml

@@ -111,7 +111,7 @@ steps:
   - name: s
     path: /var/run/docker.sock
   commands:
-  - docker-compose up -d --remove-orphans
+  - docker-compose up -d --remove-orphans -p ${DRONE_REPO_NAME}
   when:
     branch: master
     status: success