travis: increase git clone depth
travis: increase git clone depth

when --depth=50 is not enough to run your tests because `git describe`
fails to find the latest commit with a tag, it probably means that you
are not doing enough releases...

rafaelmartins/blogc,blogc/blogc,rafaelmartins/blogc,blogc/blogc,rafaelmartins/blogc,blogc/blogc