Merge branch 'release-v1.20.0'

* release-v1.20.0:
  Finish releasing v1.20.0
  Releasing v1.20.0

Author: steve-the-edwards

gradle.properties

@@ -8,7 +8,7 @@ android.useAndroidX=true
 systemProp.org.gradle.internal.publish.checksums.insecure=true
 
 GROUP=com.squareup.workflow1
-VERSION_NAME=1.20.0-SNAPSHOT
+VERSION_NAME=1.21.0-SNAPSHOT
 
 POM_DESCRIPTION=Square Workflow