Update Intl CHANGELOG.md and pubspec.yaml to prepare for 0.13.1

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=123007910
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 27e5259..5100e77 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,5 @@
+## 0.13.1
+
 ## 0.13.0
  * Add support for compact number formats ("1.2K") and for significant digits in
    number formats.
diff --git a/pubspec.yaml b/pubspec.yaml
index d0faf60..87d89fc 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: intl
-version: 0.13.0
+version: 0.13.1-dev
 author: Dart Team <misc@dartlang.org>
 description: Contains code to deal with internationalized/localized messages, date and number formatting and parsing, bi-directional text, and other internationalization issues.
 homepage: https://github.com/dart-lang/intl