Documentation uses "18.1.0" not "18.2.0"

[kou]

Describe the bug, including details regarding any error messages, version, and platform.

https://arrow.apache.org/java/18.2.0/ shows "arrow-java 18.1.0 documentation".

[kou]

We need to update

arrow-java/docs/source/conf.py

Line 29 in 34e2b08

release = '18.1.0'

by dev/release/bump-version.sh.