fix grammatical error in behind-the-block.mdx

[eniodev]

changing "But what if we another React component inside of <Emotion />{:jsx}?"

to: "But what if we had another React component inside of <Emotion />{:jsx}?"

adding: "had"

Please describe the changes this PR makes and why it should be merged:

Status

• Code changes have been tested against prettier, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Semantic versioning classification:

• This PR changes the codebase
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
  • This PR changes the internal workings with no modifications to the external API (bug fixes, performance improvements)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[coveralls]

Pull Request Test Coverage Report for Build 5150343906

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 37.323%

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Totals
Change from base Build 5148768987:	0.0%
Covered Lines:	822
Relevant Lines:	2317

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💛 - Coveralls

[aidenybai]

LGTM