fix(expo-deployment): unify reference paths to ./references/ (plural)

[xiaolai]

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Bug

plugins/expo/skills/expo-deployment/SKILL.md has an inconsistency in its reference paths. The top-level References section (lines 16–20) correctly uses ./references/ (plural), but five in-body See … links use ./reference/ (singular):

• Line 123: See ./reference/testflight.md
• Line 124: See ./reference/ios-app-store.md
• Line 130: See ./reference/play-store.md
• Line 136: See ./reference/workflows.md
• Line 165: See ./reference/workflows.md

The references/ directory exists; reference/ does not. Claude follows these links to fetch supplementary docs at load time — the singular-form links silently resolve to nothing, making half the contextual references unreachable.

Fix: Replace all ./reference/ occurrences in the body text with ./references/ to match the actual directory name and the top-level References section.