TocFilter: keep using the old punctuation stripping on 1.8.7

The UTF regexp doesn't seem to work correctly under 1.8.7 and causes
existing tests to fail. We don't really care about fixing this case
for 1.8.7 but we don't want the gem to be unusable, so we'll just
special case it for now.
Merge pull request #73 from jakedouglas/fix_ruby_1_8_anchors

TocFilter: keep using the old punctuation stripping on 1.8.7