Fixed travis build

Author: Sylvain MARIE

ci_tools/requirements-pip.txt

@@ -6,8 +6,8 @@ stdlib_list
 # --- to run the tests
 pytest  #$PYTEST_VERSION
 pytest-logging  # ==2015.11.4
-pytest_cases
-makefun==1.6.8
+pytest_cases==1.10.4  # we use that precise version otherwise there is a conflict with makefun 1.6.8
+makefun==1.6.8        # we use that precise version because it does not have the __version__ attribute.
 
 # --- to generate the reports (see scripts in ci_tools, called by .travis)
 # pytest-cov==2.6.0  # after 2.6.1 it requires pytest 3.6