EPUB: condition Blaze Utf8 module name import on blaze-html version

blaze-html/blaze-markup-0.5 has Text.Blaze.Html.Renderer.Utf8
whereas blaze-html-0.4 has Text.Blaze.Renderer.Utf8.
So this needs to be conditional on the version for pandoc
still be with blaze-html-0.4.x
Merge pull request #717 from juhp/patch-1

EPUB: condition Blaze Utf8 module name import on blaze-html version