Update numpy requirement from ~=1.20.1 to ~=1.20.3 (#51)

Updates the requirements on [numpy](https://github.com/numpy/numpy) to permit the latest version.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/main/doc/HOWTO_RELEASE.rst.txt)
- [Commits](numpy/numpy@v1.20.1...v1.20.3)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -3,7 +3,7 @@ pint~=0.17
 tabulate~=0.8.9
 path~=15.1.2
 shapely~=1.7.1
-numpy~=1.20.1
+numpy~=1.20.3
 matplotlib~=3.4.2
 pandas~=1.2.4  # because of io.common methods
 sympy==1.5.*  # because of specific expression parsing