Fixed compile error in older gcc's for trailing comma in enum.

Change-Id: I60f6da32fb2a30557fcf842624f68ca184f65e1f
Tested: on Linux.

src/flathash.cpp

@@ -23,7 +23,7 @@
 enum OutputFormat {
   kDecimal,
   kHexadecimal,
-  kHexadecimal0x,
+  kHexadecimal0x
 };
 
 int main(int argc, char* argv[]) {