add rebase merge request method

lib/gitlab/client/merge_requests.rb

@@ -337,5 +337,19 @@ def merge_request_diff_versions(project, merge_request_id)
     def merge_request_diff_version(project, merge_request_id, version_id)
       get("/projects/#{url_encode project}/merge_requests/#{merge_request_id}/versions/#{version_id}")
     end
+
+    # Rebase a merge request.
+    #
+    # @example
+    #   Gitlab.rebase_merge_request(5, 42, { skip_ci: true })
+    #
+    # @param  [Integer, String] project The ID or name of a project.
+    # @param  [Integer] id The ID of a merge request.
+    # @param  [Hash] options A customizable set of options.
+    # @option options [String] :skip_ci Set to true to skip creating a CI pipeline
+    # @return [Gitlab::ObjectifiedHash] Rebase progress status
+    def rebase_merge_request(project, id, options = {})
+      put("/projects/#{url_encode project}/merge_requests/#{id}/rebase", body: options)
+    end
   end
 end

spec/fixtures/merge_request_rebase.json

@@ -0,0 +1,3 @@
+{
+  "rebase_in_progress": true
+}

spec/gitlab/client/merge_requests_spec.rb

@@ -407,4 +407,21 @@
       expect(@diff.diffs.first['old_path']).to eq('LICENSE')
     end
   end
+
+  describe '.rebase_merge_request' do
+    before do
+      stub_put('/projects/3/merge_requests/105/rebase', 'merge_request_rebase')
+        .with(body: { skip_ci: true })
+      @response = Gitlab.rebase_merge_request(3, 105, skip_ci: true)
+    end
+
+    it 'gets correct resource' do
+      expect(a_put('/projects/3/merge_requests/105/rebase')
+        .with(body: { skip_ci: true })).to have_been_made
+    end
+
+    it 'returns rebase in progress response' do
+      expect(@response.rebase_in_progress).to be_truthy
+    end
+  end
 end