Bump intl and intl_translation versions to -dev

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=205266838
diff --git a/pubspec.yaml b/pubspec.yaml
index 10bfdf9..ad92de1 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: intl
-version: 0.15.7
+version: 0.15.7-dev
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/intl
 description: >-