Bump cairosvg from 2.1.3 to 2.5.1

Bumps [cairosvg](https://github.com/Kozea/CairoSVG) from 2.1.3 to 2.5.1.
- [Release notes](https://github.com/Kozea/CairoSVG/releases)
- [Changelog](https://github.com/Kozea/CairoSVG/blob/master/NEWS.rst)
- [Commits](Kozea/CairoSVG@2.1.3...2.5.1)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

setup.py

@@ -40,7 +40,7 @@
         'boto3==1.7.79',
         'botocore==1.10.79',
         'cairocffi==0.9.0',
-        'CairoSVG==2.1.3',
+        'CairoSVG==2.5.1',
         'celery==4.2.1',
         'certifi==2018.8.13',
         'cffi==1.13.2',