modify sed commands to handle non-GNU and GNU od

Another one-line fix :) tested on solaris, seems to generate identical browse_py.h
(with your patch, `./ninja -t browse ninja` fails for me like so:

    $ ./ninja -t browse ninja
      File "<stdin>", line 17
        " " "          S i m p l e   w e b   s e r v e          r   f o r   b r o w s i n g   d          e p e n d e n c y   g r a p h            d a t a . 
        ^
    IndentationError: unexpected indent
Note all the extra spaces.)