Prepare tools/r8_release.py for branch 2.2

Change-Id: If51a16bd5344e52282119fd6a48657ec1e82a63f
diff --git a/tools/r8_release.py b/tools/r8_release.py
index 2f3c4fc..7b1ba0b 100755
--- a/tools/r8_release.py
+++ b/tools/r8_release.py
@@ -17,7 +17,7 @@
 import archive_desugar_jdk_libs
 import utils
 
-R8_DEV_BRANCH = '2.1'
+R8_DEV_BRANCH = '2.2'
 R8_VERSION_FILE = os.path.join(
     'src', 'main', 'java', 'com', 'android', 'tools', 'r8', 'Version.java')
 THIS_FILE_RELATIVE = os.path.join('tools', 'r8_release.py')