remove nose from install_requires

[joekohlsdorf]

Nose is a test requirement, it is not necessary for users to install it.
It is listed in test-requirements.txt so removing it from install_requires should not make a difference for tests. I have reviewed the code and have not found any use of nose at runtime.

Problem description:

• The internal test requirement nose is installed when a user installs the client for runtime use.

Reproduction steps:

# docker run -it --rm --entrypoint=/bin/bash python
# pip install docusign-esign==3.14.0

Observed result:

• After running the command, the nose package is installed:

# pip freeze | grep nose
nose==1.3.7

Expected result:

• The nose package is not installed for runtime use of the docusign-esign package.