Bump pycparser from 2.19 to 2.20

Bumps [pycparser](https://github.com/eliben/pycparser) from 2.19 to 2.20. - [Release notes](https://github.com/eliben/pycparser/releases) - [Changelog](https://github.com/eliben/pycparser/blob/master/CHANGES) - [Commits](eliben/pycparser@release_v2.19...release_v2.20) Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -1,7 +1,7 @@
 atomiclong==0.1.1
 cffi==1.12.3
 fusepy==3.0.1
-pycparser==2.19
+pycparser==2.20
 pygit2==0.28.2
 raven==6.10.0
 six==1.12.0