Update Tab guidelines to match updates in demo

[mmenestr]

There have been changes to the Tab demos. We want to update the images and potentially some guidance in the tabs design guidelines to match these updates. More details around these updates and changes can be found in this marvel: https://marvelapp.com/prototype/9766ieg

Other helpful links
HTML Tab demos here: https://www.patternfly.org/v4/components/tabs/html-demos
React Tab dems here: https://www.patternfly.org/v4/components/tabs/react-demos

Original design issue: patternfly/patternfly-design#1162
Core issue: patternfly/patternfly#5058

[mmenestr]