--empty-alt-ignore option not followed

[dsernst]

I'm trying to run htmlproof with the --empty-alt-ignore option, but it doesn't seem to have any effect.

Here's an example: https://travis-ci.org/dsernst/dsernst.github.io/builds/78668326#L293. You can see on line 293 that the flag is being passed, and yet the vast majority of the html failures it reported were missing alt tags.

(I thought the extra travis_wait command might be screwing up the results, but recreating the tests on my local machine without that showed the same problem.)

[dsernst]

Ah, now re-reading the PR that introduced this feature, I realize I was misunderstanding its intent. Apologies. I'll use --alt-ignore '/.*/' instead.