Cherry-pick: ICU-21580 fix RuleBasedCollator doc typo, extra open brace

It's a pure documentation fix.

Upstream commit: https://github.com/unicode-org/icu/commit/b9bb2a7b57cbfa91427626cefc12485b3f0a4915
Upstream bug: https://unicode-org.atlassian.net/browse/ICU-21580

Bug: 191907312
Test: m droid
Merged-In: Id4aa66e02174ffc965fcdcfb87c93e2ada98d398
Change-Id: Id4aa66e02174ffc965fcdcfb87c93e2ada98d398
(cherry picked from commit f7c68b42d3b7b7700d1c103cb9552d3cbcf8ea74)
2 files changed