Bump numpy from 1.19.1 to 1.21.0 in /.binder

Bumps [numpy](https://github.com/numpy/numpy) from 1.19.1 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@v1.19.1...v1.21.0)

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

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

.binder/requirements.txt

@@ -4,7 +4,7 @@ jupyterlab>=2.2.0
 imageio
 ipywidgets>=7.5.1
 ipympl>=0.5.7
-numpy==1.19.1
+numpy==1.21.0
 matplotlib==3.3.1
 PyQt5==5.15.0
 PyQt5-sip==12.8.0