Minor bug within create_atoms.cpp

I found a minor bug in create_atoms.cpp when using "create_atoms" command with style "random".

The syntax of args should be "N seed region-ID" while the source file misleads N as seed (Line 129-130).

The corrected code of lines 129-130 is:

seed_char = new char [strlen(arg[3])+1];
strcpy(seed_char, arg[3]);

modified cpp file is attached.