bump version for next dev release

hphp/system/idl/constants.idl.json

@@ -1817,11 +1817,11 @@
         },
         {
             "name": "HPHP_VERSION",
-            "value": "2.3.0-dev"
+            "value": "2.4.0-dev"
         },
         {
             "name": "HHVM_VERSION",
-            "value": "2.3.0-dev"
+            "value": "2.4.0-dev"
         },
         {
             "name": "HTML_ENTITIES",

hphp/version

@@ -1 +1 @@
-HHVM_VERSION(2.3.0-dev)
+HHVM_VERSION(2.4.0-dev)