Use GWT 2.8.0 release version.

Author: BenDol

pom.xml

@@ -31,7 +31,7 @@
         <project.encoding>UTF-8</project.encoding>
 
         <!-- GWT -->
-        <gwt.version>2.8.0-rc1</gwt.version>
+        <gwt.version>2.8.0</gwt.version>
         <gwtp.version>1.5.3</gwtp.version>
         <gin.version>2.1.2</gin.version>
         <gwt-material.version>2.0-SNAPSHOT</gwt-material.version>