Bugfix earthengine-api

> The 2.0.0 release no longer retrieves discovery documents dynamically on each call to discovery.build(). Instead, discovery documents are retrieved from the client library itself.

See:
https://github.com/googleapis/google-api-python-client/blob/master/UPGRADING.md
https://github.com/google/earthengine-api/issues/157

```
==================================== ERRORS ====================================
________ ERROR collecting downloader_app/tests/test_tiff_downloader.py _________
downloader_app/tests/test_tiff_downloader.py:9: in
from downloader_app import tiff_downloader as td
downloader_app/tiff_downloader.py:36: in
ee.Initialize()
/opt/conda/lib/python3.7/site-packages/ee/__init__.py:123: in Initialize
http_transport=http_transport)
/opt/conda/lib/python3.7/site-packages/ee/data.py:199: in initialize
_install_cloud_api_resource()
/opt/conda/lib/python3.7/site-packages/ee/data.py:273: in _install_cloud_api_resource
http_transport=_http_transport)
/opt/conda/lib/python3.7/site-packages/ee/_cloud_api_utils.py:151: in build_cloud_resource
cache_discovery=False)
/opt/conda/lib/python3.7/site-packages/googleapiclient/_helpers.py:134: in positional_wrapper
return wrapped(*args, **kwargs)
/opt/conda/lib/python3.7/site-packages/googleapiclient/discovery.py:282: in build
static_discovery=static_discovery,
/opt/conda/lib/python3.7/site-packages/googleapiclient/discovery.py:387: in _retrieve_discovery_doc
raise UnknownApiNameOrVersion("name: %s version: %s" % (serviceName, version))
E googleapiclient.errors.UnknownApiNameOrVersion: name: earthengine version: v1alpha
=============================== warnings summary ===============================
/opt/conda/lib/python3.7/site-packages/rasterstats/io.py:24
/opt/conda/lib/python3.7/site-packages/rasterstats/io.py:24
/opt/conda/lib/python3.7/site-packages/rasterstats/io.py:24: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3,and in 3.9 it will stop working
from collections import Iterable, Mapping

/opt/conda/lib/python3.7/site-packages/holoviews/operation/datashader.py:5
/opt/conda/lib/python3.7/site-packages/holoviews/operation/datashader.py:5: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3,and in 3.9 it will stop working
from collections import Callable

-- Docs: https://docs.pytest.org/en/stable/warnings.html
=========================== short test summary info ============================
ERROR downloader_app/tests/test_tiff_downloader.py - googleapiclient.errors.U...
!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!
========================= 3 warnings, 1 error in 8.92s =========================
make: *** [docker/satellite/Makefile:53: test_downloader_app] Error 2
Error: Process completed with exit code 2.
```