fix(.gitattributes): set "eol=lf" only for known text files

Previously only .exe files wasn't "text", every other file got
a "eol=lf" rule.
See 5b03fac3a30b14745b0a3f839b1d05c744685fc6.

There's a .png file now which should also be considered binary.

It's quite easy to forget to add new extensions to "binary" category,
so let's set "eol=lf" explicitly only for known file extensions.

Also amend source/meta/logo.png which was affected.

This closes #132.