Fix syntax error

[zouppen]

There is syntax error in transaction.py. I made quick fix and it seems to work. Please test before merging because I didn't test this fix carefully.

[reiven]

+1 @vbuterin please merge this, is making pybtctool fails

Traceback (most recent call last):
  File "./pybtctool", line 3, in <module>
    from bitcoin import *
  File "/tmp/pybitcointools/bitcoin/__init__.py", line 4, in <module>
    from bitcoin.transaction import *
  File "/tmp/pybitcointools/bitcoin/transaction.py", line 141
    for out in newtx["outs'][:len(newtx["ins"]) - 1)]:
                                           ^

[wizardofozzie]

Yep, that was mistyped from my PR.
Signing of SIGHASH_SINGLE should also be returning 1 for outputs at an index larger than the input index, though I'll make a separate issue

[reiven]

Thanks @vbuterin !