[deps] Constrain numpy version to <= 1.18.3

[valeriocos]

The numpy dependency is constrained to <= 1.18.3. This change is needed since from version 1.19.x the support for python 3.5 has been discontinued.

Refs:

• https://numpy.org/devdocs/release/1.19.0-notes.html#id1
• https://github.com/numpy/numpy/issues/16294

[coveralls]

Pull Request Test Coverage Report for Build 2277

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 81.886%

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Totals
Change from base Build 2274:	0.0%
Covered Lines:	8146
Relevant Lines:	9948

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💛 - Coveralls