Follow renaming from CE

See
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13739

app/services/merge_requests/ff_merge_service.rb

@@ -13,7 +13,7 @@ module MergeRequests
                           source,
                           merge_request.target_branch,
                           merge_request: merge_request)
-    rescue GitHooksService::PreReceiveError => e
+    rescue Gitlab::Git::HooksService::PreReceiveError => e
       raise MergeError, e.message
     rescue StandardError => e
       raise MergeError, "Something went wrong during merge: #{e.message}"

app/services/projects/update_mirror_service.rb

@@ -50,7 +50,7 @@ module Projects
         else
           begin
             repository.ff_merge(current_user, upstream_branch.dereferenced_target, name)
-          rescue GitHooksService::PreReceiveError, Repository::CommitError => e
+          rescue Gitlab::Git::HooksService::PreReceiveError, Repository::CommitError => e
             errors << e.message
           end
         end

spec/services/merge_requests/ff_merge_service_spec.rb

@@ -71,7 +71,7 @@ describe MergeRequests::FfMergeService do
       it 'logs and saves error if there is an PreReceiveError exception' do
         error_message = 'error message'
 
-        allow(service).to receive(:repository).and_raise(GitHooksService::PreReceiveError, error_message)
+        allow(service).to receive(:repository).and_raise(Gitlab::Git::HooksService::PreReceiveError, error_message)
         allow(service).to receive(:execute_hooks)
 
         service.execute(merge_request)