Update the version to 1.21 in preparation for a new release.

PiperOrigin-RevId: 241053616
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 934f15a..e471a2a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,6 +3,7 @@
 # found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 cmake_minimum_required(VERSION 3.9)
+# Keep the version below in sync with the one in db.h
 project(leveldb VERSION 1.21.0 LANGUAGES C CXX)
 
 # This project can use C11, but will gracefully decay down to C89.
diff --git a/include/leveldb/db.h b/include/leveldb/db.h
index 84c32bc..0239593 100644
--- a/include/leveldb/db.h
+++ b/include/leveldb/db.h
@@ -13,9 +13,9 @@
 
 namespace leveldb {
 
-// Update Makefile if you change these
+// Update CMakeLists.txt if you change these
 static const int kMajorVersion = 1;
-static const int kMinorVersion = 20;
+static const int kMinorVersion = 21;
 
 struct Options;
 struct ReadOptions;