Update `requests` library to 1.2.3

common/djangoapps/terrain/browser.py

common/lib/capa/capa/xqueue_interface.py

common/lib/sample-post.py

...dule/open_ended_grading_classes/grading_service_module.py

docs/shared/requirements.txt

...pps/courseware/mock_youtube_server/mock_youtube_server.py

lms/djangoapps/instructor/tests/test_api.py

lms/djangoapps/instructor/views/api.py

requirements/edx/base.txt