Fix an "allows to" grammar nit

Thanks again for writing and maintaining microsocks! Here's a trivial change that follows the common English usage of "allow" - unlike some Slavic languages (trust me, I know :)), it should be used with an object, e.g. "allows one to", "allows you to", "allows the user to". I think that in these cases it is not needed at all, since the description of the other command-line options use "specifies" directly.