elastic based on the latest builds instead of the oldest

Author: tshibata

src/main/java/hudson/plugins/build_timeout/BuildTimeoutWrapper.java

@@ -207,7 +207,7 @@ private static double averageDuration(List <Run> builds) {
         int nonFailingBuilds = 0;
         int durationSum= 0;
 
-        for (int i = builds.size() - 1; i >= 0 && nonFailingBuilds < NUMBER_OF_BUILDS_TO_AVERAGE; i--) {
+        for (int i = 0; i < builds.size() && nonFailingBuilds < NUMBER_OF_BUILDS_TO_AVERAGE; i++) {
             Run run = builds.get(i);
             if (run.getResult() != null && 
                     run.getResult().isBetterOrEqualTo(Result.UNSTABLE)) {