MAINT: update v3.2 changelog entry
# Altair Change Log
## Version 3.2.0 (unreleased)
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+Upgraded to Vega-Lite version 3.4 (See [Vega-Lite 3.4 Release Notes](https://github.com/vega/vega-lite/releases/tag/v3.4.0)).
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+Following are changes to Altair in addition to those that came with VL 3.4:
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### Enhancements
- Selector values can be used directly in expressions (#1599)
