Update the versions of protobuf, asm and guava libraries

These updates are needed to synchronize with the versions used
in GWT 2.6.0

Change-Id: Ie17901c0fa7c30317708b16e548b95bc84960cfd
diff --git a/pom.xml b/pom.xml
index 86bc69c..20df4ca 100644
--- a/pom.xml
+++ b/pom.xml
@@ -319,14 +319,14 @@
     <dependency>
       <groupId>org.ow2.asm</groupId>
       <artifactId>asm</artifactId>
-      <version>4.0</version>
+      <version>4.1</version>
       <scope>compile</scope>
     </dependency>
 
     <dependency>
       <groupId>com.google.guava</groupId>
       <artifactId>guava</artifactId>
-      <version>13.0.1</version>
+      <version>15.0</version>
       <scope>compile</scope>
     </dependency>
 
@@ -375,7 +375,7 @@
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java</artifactId>
-      <version>2.4.1</version>
+      <version>2.5.0</version>
       <scope>provided</scope>
     </dependency>
   </dependencies>