librato.exceptions.Unauthorized when using `lore api`

```
Exception in thread Thread-3:
Traceback (most recent call last):
File "/app/.heroku/python/lib/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/app/.heroku/python/lib/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/app/.heroku/python/lib/python3.6/site-packages/librato/aggregator.py", line 191, in submit
query_props=self.to_payload())
File "/app/.heroku/python/lib/python3.6/site-packages/librato/__init__.py", line 209, in _mexe
resp_data, success, backoff = self._process_response(resp, backoff)
File "/app/.heroku/python/lib/python3.6/site-packages/librato/__init__.py", line 183, in _process_response
raise exceptions.get(resp.status, resp_data)
librato.exceptions.Unauthorized: [401] Credentials are required to access this resource.
10:56:55.911 WARNING threading:120 => Exception in thread Thread-3:
Traceback (most recent call last):
File "/app/.heroku/python/lib/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/app/.heroku/python/lib/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/app/.heroku/python/lib/python3.6/site-packages/librato/aggregator.py", line 191, in submit
query_props=self.to_payload())
File "/app/.heroku/python/lib/python3.6/site-packages/librato/__init__.py", line 209, in _mexe
resp_data, success, backoff = self._process_response(resp, backoff)
File "/app/.heroku/python/lib/python3.6/site-packages/librato/__init__.py", line 183, in _process_response
raise exceptions.get(resp.status, resp_data)
librato.exceptions.Unauthorized: [401] Credentials are required to access this resource.
```