use diamond operator

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1916036 13f79535-47bb-0310-9956-ffa450edef68

poi-ooxml/src/main/java/org/apache/poi/xddf/usermodel/chart/Grouping.java

@@ -32,7 +32,7 @@ public enum Grouping {
         this.underlying = grouping;
     }
 
-    private static final HashMap<STGrouping.Enum, Grouping> reverse = new HashMap<STGrouping.Enum, Grouping>();
+    private static final HashMap<STGrouping.Enum, Grouping> reverse = new HashMap<>();
     static {
         for (Grouping value : values()) {
             reverse.put(value.underlying, value);