Simplify and speedup VulnerabilityMetricsUpdateTask with safe aliases

Signed-off-by: Valentijn Scholten <valentijnscholten@gmail.com>

src/main/java/org/dependencytrack/tasks/metrics/VulnerabilityMetricsUpdateTask.java

@@ -120,7 +120,7 @@ private static Collection<YearMonthMetric> queryForMetrics(PersistenceManager pm
         // You cannot seem to use IF ELSE with GROUP BY in JDOQL
         // So we end up doing two queries instead of one with an IF ELSE
         String queryTemplate =
-            "SELECT %s.getYear() as year, %s.getMonth()+1 as month, count(this) as count " + 
+            "SELECT %s.getYear() as y, %s.getMonth()+1 as m, count(this) as count " + 
             "FROM org.dependencytrack.model.Vulnerability " +
             "WHERE %s != null && %s == null " +
             "GROUP BY %s.getYear(), %s.getMonth() + 1";