Bump pygments from 2.3.1 to 2.7.4

Bumps [pygments](https://github.com/pygments/pygments) from 2.3.1 to 2.7.4.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.3.1...2.7.4)

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==2.3.1
+Pygments==2.7.4
 Quandl==3.4.5
 asn1crypto==0.24.0
 backcall==0.1.0