tumblr.py: update regex for video (#133)

There seems to be another sub-domain for videos, apparently..
Not just
`vt(.media).tumblr`
`vtt(media).tumblr`
But also
`ve(.media).tumblr`

gallery_dl/extractor/tumblr.py

@@ -25,7 +25,7 @@ def _original_inline_image(url):
 
 def _original_video(url):
     return re.sub(
-        (r"https?://(vt+(?:\.media)?\.tumblr\.com"
+        (r"https?://((?:vt|vtt|ve)(?:\.media)?\.tumblr\.com"
          r"/tumblr_[^_]+)_\d+\.([0-9a-z]+)"),
         r"https://\1.\2", url
     )