Update the exonum version in the examples:

0.12.0 -> 0.13.0-rc.2

Author: dmitry-timofeev

exonum-java-binding/exonum_launcher_java_plugins/README.md

@@ -74,10 +74,10 @@ artifacts:
       artifact_filename: "exonum-java-binding-cryptocurrency-demo-0.9.0-rc1-artifact.jar"
   time:
     runtime: rust
-    name: "exonum-time:0.12.0"
+    name: "exonum-time:0.13.0-rc.2"
   timestamping:
     runtime: rust
-    name: "exonum-timestamping:0.12.0"
+    name: "exonum-timestamping:0.13.0-rc.2"
 ```
 
 Add a `plugins` section to enable both Java Runtime plugin and Instance Configuration plugin.

exonum-java-binding/exonum_launcher_java_plugins/sample-config.yml

@@ -23,10 +23,10 @@ artifacts:
       artifact_filename: "exonum-java-binding-cryptocurrency-demo-0.9.0-rc1-artifact.jar"
   time:
     runtime: rust
-    name: "exonum-time:0.12.0"
+    name: "exonum-time:0.13.0-rc.2"
   timestamping:
     runtime: rust
-    name: "exonum-timestamping:0.12.0"
+    name: "exonum-timestamping:0.13.0-rc.2"
 
 instances:
   cryptocurrency: