Fix rebase check

Increase the depth of the shallow clone done by GitLab.
If the number of commits is larger than the depth, the head of the
upstream/master is not in the history otherwise.
This fixes a problem of !399.

.gitlab-ci.yml

@@ -8,7 +8,7 @@ stages:
 RebaseCheck:
   stage: checkRepository
   variables:
-    GIT_DEPTH: 100
+    GIT_DEPTH: 200
   image: alpine
   tags:
     - docker
@@ -41,7 +41,7 @@ RebaseCheck:
 LinearHistCheck:
   stage: checkRepository
   variables:
-    GIT_DEPTH: 100
+    GIT_DEPTH: 200
   image: alpine
   tags:
     - docker