StringBuffer -> StringBuilder

Change-Id: Ibacf9357619712909544ddeb901bbef04c822bfe
diff --git a/utils/misc/src/main/java/org/onlab/packet/IPv4.java b/utils/misc/src/main/java/org/onlab/packet/IPv4.java
index b8b58bc..95695dc 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IPv4.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IPv4.java
@@ -511,7 +511,7 @@
      * @return string form of ip address
      */
     public static String fromIPv4Address(final int ipAddress) {
-        final StringBuffer sb = new StringBuffer();
+        final StringBuilder sb = new StringBuilder();
         int result = 0;
         for (int i = 0; i < 4; ++i) {
             result = ipAddress >> (3 - i) * 8 & 0xff;
@@ -537,7 +537,7 @@
         if (ipAddresses == null) {
             return "null";
         }
-        final StringBuffer sb = new StringBuffer();
+        final StringBuilder sb = new StringBuilder();
         sb.append("[");
         for (final Integer ip : ipAddresses) {
             sb.append(IPv4.fromIPv4Address(ip));