Bump ipython from 5.1.0 to 7.16.3 in /server

Bumps [ipython](https://github.com/ipython/ipython) from 5.1.0 to 7.16.3.
- [Release notes](https://github.com/ipython/ipython/releases)
- [Commits](https://github.com/ipython/ipython/compare/5.1.0...7.16.3)

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

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

server/requirements.txt

@@ -2,4 +2,4 @@ tensorflow==0.12.1
 magenta==0.1.8
 Flask==0.12
 gunicorn==19.6.0
-ipython==5.1.0
+ipython==7.16.3