Updated and pinned version for requests

[cmonr]

Description

A CVE was made public about a possible vulnerability involving the requests python module.

Version has been updated to latest secure version, with pinning added to not auto increase past patch releases.

Testing

Tested in Linux using Py2 and Py3 pipenv environments by running pip install -r requirements.txt in each.

Windows testing ongoing.

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[cmonr]

Rebased and re-tested.

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3527
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8616/

Triggering tests

/morph test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 3144
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8616/

[mbed-ci]

Test : SUCCESS

Build number : 3315
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8616/3315