Merge envars before sending a request (#729)

Taken from the `requests` docs:

https://requests.readthedocs.io/en/latest/user/advanced/#prepared-requests

Fixes #727

Author: stevemessick

kagglesdk/kaggle_http_client.py

@@ -119,7 +119,9 @@ def call(
     self._init_session()
     http_request = self._prepare_request(service_name, request_name, request)
 
-    http_response = self._session.send(http_request)
+    # Merge environment settings into session
+    settings = self._session.merge_environment_settings(http_request.url, {}, None, None, None)
+    http_response = self._session.send(http_request, **settings)
 
     response = self._prepare_response(response_type, http_response)
     return response

src/kagglesdk/kaggle_http_client.py

@@ -119,7 +119,9 @@ def call(
     self._init_session()
     http_request = self._prepare_request(service_name, request_name, request)
 
-    http_response = self._session.send(http_request)
+    # Merge environment settings into session
+    settings = self._session.merge_environment_settings(http_request.url, {}, None, None, None)
+    http_response = self._session.send(http_request, **settings)
 
     response = self._prepare_response(response_type, http_response)
     return response