Add a secret key base for sessions to please rails

g5k-api does not use sessions !

config/initializers/secret_token.rb

+# coding: utf-8
+# Copyright (c) 2018 David Margery, INRIA Rennes - Bretagne Atlantique
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+Api::Application.config.secret_key_base = 'Ne sert à rien, nous n\'utilisons pas de sessions'