Removed PHP 5.3 build option

Added experimental hhvm build option.

.travis.yml

@@ -1,6 +1,6 @@
 # The MIT License (MIT)
 # 
-# Copyright (c) 2011-2014 BitPay
+# Copyright (c) 2011-2015 BitPay
 # 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -21,9 +21,10 @@
 # THE SOFTWARE.
 language: php
 php:
+    - 5.6
     - 5.5
     - 5.4
-    - 5.3
+    - hhvm
 install:
     - composer install
 #script: ./bin/phing -verbose -propertyfile build/travis.properties build-travis
@@ -37,4 +38,4 @@ cache:
 matrix:
     fast_finish: true
     allow_failures:
-        - php: 5.3
+        - php: hhvm