Update access of neighbor distances from Anndata

Need a fix for deprecation warning

```
 self.func_ir.loc))
/home/ec2-user/anaconda3/envs/python3/lib/python3.6/site-packages/palantir/utils.py:43: FutureWarning: This location for 'distances' is deprecated. It has been moved to .obsp[distances], and will not be accesible here in a future version of anndata.
  kNN = temp.uns['neighbors']['distances']

```