bump repo2docker to 0.11

[scottyhq]

trying this again with new package versions

[scottyhq]

pangeo-notebook build failing with lots of conda package compatibility messages ultimately failing with:

Some log outputs:

Warning: you have pip-installed dependencies in your environment file, but you do not list pip itself as one of your conda dependencies.  Conda may not use the correct pip to install your packages, and they may end up in the wrong place.  Please add an explicit pip dependency.  I'm adding one for you, but still nagging you.
Collecting package metadata (repodata.json): ...working... done
Solving environment: ...working... 
Finding conflicts:   0%|          | 0/569 [00:00<?, ?it/s]
Examining nomkl:   0%|          | 0/569 [00:00<?, ?it/s]  
Examining harfbuzz:   0%|          | 1/569 [00:00<00:00, 2906.66it/s]
Examining nodejs:   0%|          | 2/569 [00:00<00:00, 3501.09it/s] 

UnsatisfiableError: The following specifications were found to be incompatible with a past
explicit spec that is not an explicit spec in this operation (dask):
  - dask-ml -> dask[version='>=0.18.2|>=1.0.0']

The following specifications were found to be incompatible with each other:
Package numpy conflicts for:
seaborn -> numpy[version='>=1.13.3|>=1.9.3']

Traceback (most recent call last):
  File "/usr/local/bin/r2d_overlay.py", line 147, in <module>
    main()
  File "/usr/local/bin/r2d_overlay.py", line 141, in main
    build()
  File "/usr/local/bin/r2d_overlay.py", line 109, in build
    ['/bin/bash', '-c', command], preexec_fn=applicator._pre_exec
  File "/srv/conda/envs/notebook/lib/python3.7/subprocess.py", line 363, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['/bin/bash', '-c', 'conda env update -p /srv/conda/envs/notebook -f /home/jovyan/.onbuild-child/binder/environment.yml']' returned non-zero exit status 1.
The command '/bin/sh -c /usr/local/bin/r2d_overlay.py build' returned a non-zero code: 1

The main change I think from repo2docker 0.10 to 0.11 is conda going from 4.7.10 to 4.7.12 jupyterhub/repo2docker#802

Not planning on sorting this out until #125 is sorted