lfs: add the 'Content-Type' header called out in the file transfer spec

https://github.com/git-lfs/git-lfs/blob/master/docs/api/basic-transfers.md#uploads

hgext/lfs/blobstore.py

@@ -332,6 +332,7 b' class _gitlfsremote(object):'
                                   hint=_('run hg verify'))
             request.data = filewithprogress(localstore.open(oid), None)
             request.get_method = lambda: 'PUT'
+            request.add_header('Content-Type', 'application/octet-stream')
 
         for k, v in headers:
             request.add_header(k, v)