Changed 'default' and 'html5' templates to use 'current_page.data.title' instead of 'data.page.title'

Since `data.page.title` seems broken (according to https://github.com/middleman/middleman-blog/issues/107#issuecomment-14944013), this PR changes the 'default' and 'html5' templates to use `current_page.data.title` instead.

Since the number of failing tests is the same before and after this modification, I guess the build not passing the tests is not related to this very PR (furthermore, the templates does not seem to be tested at all).