ci: add .git to the Docker container

Because commitlint needs a .git repository to lint all commits on a branch, we're adding it to the
Docker container.

re #121

.gitlab-ci.yml

@@ -46,7 +46,7 @@ lint:commits:
    stage: test
    script:
      - cd ${HOME}
-     - yarn commitlint --from=master --to=$CI_COMMIT_REF_NAME
+     - yarn commitlint --from=origin/master --to=$CI_COMMIT_SHA
 
 test:
   image: $IMAGE_ORG/$IMAGE_NAME:$CI_COMMIT_SHA

Dockerfile

@@ -3,6 +3,7 @@ FROM pubsweet/pubsweet:base
 COPY package.json yarn.lock ./
 COPY lerna.json .eslintignore .eslintrc .prettierrc .stylelintignore .stylelintrc ./
 COPY packages packages
+COPY .git .git
 
 RUN [ "yarn", "config", "set", "workspaces-experimental", "true" ]