erlang:split_binary/2 docfix

[Aleksey Yeschenko]

http://github.com/iamaleksey/otp/tree/split_binary_docfix

Fixes split_binary documentation. 0 is a valid value for the Pos argument:

1> split_binary(<<1,2,3,4>>, 0).
{<<>>,<<1,2,3,4>>}

A one byte change (one bit, actually), doesnt' break anything (obviously).