Release Tsunami Security Scanner to 0.0.21

Author: tooryx

build.gradle

@@ -13,7 +13,7 @@ subprojects {
     apply plugin: 'net.ltgt.errorprone'
 
     group = 'com.google.tsunami'
-    version = '0.0.21-SNAPSHOT' // Current Tsunami version
+    version = '0.0.21' // Current Tsunami version
 
     repositories {
         maven { // The google mirror is less flaky than mavenCentral()