Update V8 to r3431 as required by WebKit r51976.

Change-Id: I567392c3f8c0a0d5201a4249611ac4ccf468cd5b
diff --git a/src/version.cc b/src/version.cc
index 54e688b..3611d44 100644
--- a/src/version.cc
+++ b/src/version.cc
@@ -32,9 +32,9 @@
 // These macros define the version number for the current version.
 // NOTE these macros are used by the SCons build script so their names
 // cannot be changed without changing the SCons build script.
-#define MAJOR_VERSION     1
-#define MINOR_VERSION     3
-#define BUILD_NUMBER      17
+#define MAJOR_VERSION     2
+#define MINOR_VERSION     0
+#define BUILD_NUMBER      4
 #define PATCH_LEVEL       0
 #define CANDIDATE_VERSION true