Add missing packages to requirements.txt

[adriangonz]

Fixes #858, adding the missing dependencies.

[seldondev]

Hi @adriangonz. Thanks for your PR.

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[ukclivecox]

/approve

[seldondev]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cliveseldon

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[ukclivecox]

/ok-to-test

[ukclivecox]

/retest