Upgrade babel-plugin-react-docgen

[danielduan]

Issue: storybookjs/babel-plugin-react-docgen#67

What I did

• Add support for forwardRef functions
• Upgrade react-docgen to pull in new features
• Upgrade lodash to fix security vulerability

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

If your answer is yes to any of these, please make sure to include it in your PR.

[codecov]

Codecov Report

Merging #6317 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6317   +/-   ##
=======================================
  Coverage   35.06%   35.06%           
=======================================
  Files         636      636           
  Lines        9366     9366           
  Branches     1343     1320   -23     
=======================================
  Hits         3284     3284           
  Misses       5436     5436           
  Partials      646      646

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[danielduan]

@ndelangen am I still good to merge with these failing builds?

[shilman]

@danielduan I merged this and then reverted it. PRs should be directed at the next branch. Will create a new PR now.