ci: unpin robotframework and update robotframework-lint to 1.1

This reverts workaround from d8c6e3d commit and pins
robotframework-lint in order to prevent CI failures after uncontrolled update in future.

Follow-up to #1404

Author: php-coder

.travis.yml

@@ -21,7 +21,7 @@ before_script:
       mkdir -p /tmp/uploads /tmp/preview;
       cp src/main/resources/test/test.png /tmp/uploads/1.png;
       npm install -g bootlint;
-      pip install --user html5validator==0.3.1 robotframework==3.1.2 robotframework-lint ansible==2.9.2 ansible-lint;
+      pip install --user html5validator==0.3.1 robotframework-lint==1.1 ansible==2.9.2 ansible-lint;
       if [ "$TRAVIS_PULL_REQUEST" != 'false' ]; then
         gem install danger nokogiri --no-ri --no-rdoc;
       fi;