Remove --use-mirrors from pip install calls
Remove --use-mirrors from pip install calls

Latest versions of pip do not support --use-mirrors

edx/js-test-tool,edx/js-test-tool,kyroskoh/js-test-tool,edx/js-test-tool,edx/js-test-tool,kyroskoh/js-test-tool,kyroskoh/js-test-tool,kyroskoh/js-test-tool