Make a 0.15.8 version

PiperOrigin-RevId: 239817439
diff --git a/pubspec.yaml b/pubspec.yaml
index ff78df7..d811a0b 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: intl
-version: 0.15.8-dev
+version: 0.15.8
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/intl
 description: >-