Update react-apollo-migration.md

[yalamber]

wrap Apollo consumer example in a div.

Checklist:

• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests

[apollo-cla]

@yalamber: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[hwillson]

Thanks @yalamber!

[codecov]

Codecov Report

Merging #3819 into master will increase coverage by 1.53%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3819      +/-   ##
==========================================
+ Coverage   87.64%   89.18%   +1.53%     
==========================================
  Files          32       43      +11     
  Lines        1757     2357     +600     
  Branches      434      564     +130     
==========================================
+ Hits         1540     2102     +562     
- Misses        203      239      +36     
- Partials       14       16       +2

Impacted Files	Coverage Δ
packages/apollo-cache-inmemory/src/index.ts	100% <0%> (ø)
packages/apollo-cache/src/cache.ts	100% <0%> (ø)
packages/apollo-boost/src/index.ts	88.7% <0%> (ø)
packages/apollo-cache-inmemory/src/objectCache.ts	100% <0%> (ø)
packages/apollo-cache/src/utils.ts	100% <0%> (ø)
...ackages/apollo-cache-inmemory/src/readFromStore.ts	97.72% <0%> (ø)
packages/apollo-cache-inmemory/src/writeToStore.ts	98.13% <0%> (ø)
...kages/apollo-cache-inmemory/src/fragmentMatcher.ts	90.9% <0%> (ø)
...ckages/apollo-cache-inmemory/src/recordingCache.ts	86.2% <0%> (ø)
packages/apollo-cache-inmemory/src/mapCache.ts	100% <0%> (ø)
... and 1 more

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