Update OpenML requirement to 0.3.3 in /docs

[dependabot]

Updates the requirements on OpenML to permit the latest version.

Release notes

Sourced from OpenML's releases.

v0.3.3

OpenML v0.3.3

Diff since v0.3.2

Merged pull requests:

• Extend JSON compat to include "1.0" (#31) (@​ablaom)
• For a 0.3.3 release (#32) (@​ablaom)
• Simplify doc generation logic (#33) (@​ablaom)

Closed issues:

• Allow upgrade of JSON.jl compat (#30)

Commits

• 6b35d5a Merge pull request #32 from JuliaAI/dev
• 070bfa3 dummy commit
• 7414b9d Merge pull request #33 from JuliaAI/doc-ci-simplification
• d765333 typo
• f8a3e8e simplify doc generation logic
• cd2d6d3 bump Documenter version, dump unsupported DocumenterMarkdown
• fa687a0 bump 0.3.3
• d5d8fe3 Merge pull request #31 from JuliaAI/json-compat-extend
• 21e3537 rm all traces of these redundant tests
• cd95076 rm more of the same
• Additional commits viewable in compare view

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