Bump pygments from 2.7.4 to 2.15.0

Bumps [pygments](https://github.com/pygments/pygments) from 2.7.4 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.7.4...2.15.0)

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

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

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 Keras==2.2.4
 Keras-Preprocessing==1.0.5
 PySocks==1.6.8
-Pygments==2.7.4
+Pygments==2.15.0
 Quandl==3.4.5
 asn1crypto==0.24.0
 backcall==0.1.0