updating confluent version to enable hosted SR (#209)

see #208

Author: MosheBlumbergX

build.gradle

@@ -19,7 +19,7 @@ project.ext {
     googleCloudVersion = '1.79.0'
     googleAuthVersion = '0.9.0'
     googleCloudGsonVersion = '2.8.5'
-    ioConfluentVersion = '5.1.1'
+    ioConfluentVersion = '5.3.1'
     junitVersion = '4.12'
     kafkaVersion = '2.3.0'
     mockitoVersion = '1.10.19'