Bump ipython from 2.1.0 to 7.16.3 in /docs

Bumps [ipython](https://github.com/ipython/ipython) from 2.1.0 to 7.16.3.
- [Release notes](https://github.com/ipython/ipython/releases)
- [Commits](ipython/ipython@rel-2.1.0...7.16.3)

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

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

docs/requirements.txt

@@ -1,4 +1,4 @@
-ipython==2.1.0
+ipython==7.16.3
 matplotlib==1.3.1
 numpy==1.8.1
 scipy==0.13.3