Update datehistogram-aggregation.asciidoc

[jmucero97]

There is an error on the sign of the timezone, when we're in UTC - 1, our midnight occurs 1h AFTER midnight in UTC.

For the statement to be correct, it should be in UTC + 1 (Timezone of Madrid in winter)

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Pinging @elastic/es-docs (Team:Docs)

[abdonpijpelink]

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[leemthompo]

Important

Elastic documentation is migrating to Markdown for version 9.0+. See the migration guide for details.

ℹ️ What's happening?

• Starting January 29, we will start closing all unmerged documentation PRs targeting main/master
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Option 1:

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Option 2:

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