A better fix for #153.

Since we're building Tink with Protobuf 3.6.0, we should also depend on this version at runtime.

PiperOrigin-RevId: 221251377
GitOrigin-RevId: d9359867812f5e9fa600c33c059c2f80d5b221b2
diff --git a/maven/tink.pom.xml b/maven/tink.pom.xml
index 9e2b0c9..c89e6af 100644
--- a/maven/tink.pom.xml
+++ b/maven/tink.pom.xml
@@ -71,7 +71,7 @@
     <google-auto-service.version>1.0-rc4</google-auto-service.version>
     <google-guava.version>25.0-jre</google-guava.version>
     <json.version>20170516</json.version>
-    <protobuf.version>3.4.0</protobuf.version>
+    <protobuf.version>3.6.0</protobuf.version>
     <protobuf-lite.version>3.0.1</protobuf-lite.version>
   </properties>