Bump numpy from 1.15.2 to 1.21.0

Bumps [numpy](https://github.com/numpy/numpy) from 1.15.2 to 1.21.0.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/main/doc/HOWTO_RELEASE.rst.txt)
- [Commits](numpy/numpy@v1.15.2...v1.21.0)

---
updated-dependencies:
- dependency-name: numpy
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -19,7 +19,7 @@ jedi==0.13.2
 kiwisolver==1.0.1
 matplotlib==3.0.0
 more-itertools==5.0.0
-numpy==1.15.2
+numpy==1.21.0
 pandas==0.23.4
 patsy==0.5.0
 pexpect==4.6.0