Update to React 16

[thedrew12]

Fixes https://github.com/diegohaz/arc/issues/320

• updated to React 16
• dropped some tests from the src-example which were breaking
• added a setup test file to work with React 16 and the latest enzyme

[Geczy]

You need to add this step too: https://github.com/facebook/jest/issues/4545#issuecomment-332762365

[codecov-io]

Codecov Report

Merging #323 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #323   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          43     44    +1     
  Lines         297    289    -8     
  Branches       56     56           
=====================================
- Hits          297    289    -8

Impacted Files	Coverage Δ
private/jest/shim.js	100% <100%> (ø)
private/jest/setupTests.js	100% <100%> (ø)
...-example/components/molecules/CodeSponsor/index.js

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[diegohaz]

Thank you so much, @thedrew12