Make the version be 1.2.0. (#59)

We haven't released 1.2.0 yet, so making it 1.2.1 is unnecessary.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4aa15dc..cb264be 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,9 +1,6 @@
-## 1.2.1
-
-* Fix `Characters.where` which unnecessarily did the iteration and test twice.
-
 ## 1.2.0
 
+* Fix `Characters.where` which unnecessarily did the iteration and test twice.
 * Adds `Characters.empty` constant and makes `Characters("")` return it.
 * Changes the argument type of `Characters.contains` to (covariant) `String`.
   The implementation still accepts `Object?`, so it can be cast to
diff --git a/pubspec.yaml b/pubspec.yaml
index 90d1ca0..065c191 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: characters
-version: 1.2.1
+version: 1.2.0
 description: String replacement with operations that are Unicode/grapheme cluster aware.
 repository: https://www.github.com/dart-lang/characters