gradle: update zxing

Change-Id: Ie0eed213b44e41a54439c47c296d726bf42ff183
diff --git a/ring-android/libringclient/build.gradle b/ring-android/libringclient/build.gradle
index a8464a7..f2a0301 100644
--- a/ring-android/libringclient/build.gradle
+++ b/ring-android/libringclient/build.gradle
@@ -8,7 +8,7 @@
     compile 'com.googlecode.ez-vcard:ez-vcard:0.10.4'
 
     // QRCode encoding
-    compile 'com.google.zxing:core:3.3.2'
+    compile 'com.google.zxing:core:3.3.3'
 
     // dependency injection
     compile 'javax.inject:javax.inject:1'