Latest updated from exoplanet removes gp module.

[jejjohnson]

Issue

Got an error when using the latest exoplanet package (0.4.0)

File "/home/jemanjohnson34/projects/dot/dot/model.py", line 5, in <module>
    from exoplanet.gp import terms, GP
  File "/opt/conda/envs/dotenv_gcp/lib/python3.8/site-packages/exoplanet/gp.py", line 1, in <module>
    raise ImportError(
ImportError: The 'gp' submodule has been removed; use 'celerite2' instead: https://github.com/dfm/celerite2

After checking the release, found that the latest update has dropped the gp from the package and instead uses the celerite2 package.

Noticeable Code Change

The API has changed slightly as there is no gp.marginal method for us like in version 0.3. Will have to go through the new tutorial to see what's changed.

Suggestions

1. We can go through and update everything to the newest version, 0.4.
2. We just use the previous version, 0.3.
3. I couldn't find the exoplanet requirement nor an explicit requirements file in the celerite branch so I guess that maybe why I stumbled on this as I was using an updated environment_gcp.yml file.

Fix

For now, I made the exoplanet package 0.3 for now. Below is the environment_gcp.yml file.

Details

name: dotenv_gcp
channels:
  - anaconda
dependencies:
  - python=3.8
  - numpy>=1.19
  - pandas>=1.1
  - astropy>3.2.1
  - conda-forge::lightkurve
  - h5py>=2.10
  - conda-forge::pymc3
  - conda-forge::celerite
  - matplotlib>=3.3
  - seaborn>=0.11
  - pip
  - pip:
    - wandb
    - tqdm
    - mypy
    - corner
    - exoplanet==0.3.3
    - google-cloud-storage>1.16