Pin robotframework-robocop version in tox.ini to 4.2.2 to fix stage2

Change-Id: I20e2c99974aeca202432d0473e585796001b7568
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>

tox.ini

@@ -66,7 +66,7 @@ changedir = {toxinidir}/robot-systest
 deps =  {[testenv]deps}
         -r{toxinidir}/requirements-dev.txt
         robotframework-lint
-        robotframework-robocop
+        robotframework-robocop==4.2.2
 commands =
         rflint --ignore LineTooLong --ignore TooFewTestSteps --ignore TooManyTestCases \
                --ignore TooManyTestSteps --ignore TooFewKeywordSteps \