requirements: update 'jsonschema'

Also, a dependency is marked as conditional, based on
https://github.com/Julian/jsonschema/blob/v3.2.0/setup.cfg#L31

Changelog:
- 3.2.0 (2019-11-18)
  https://github.com/Julian/jsonschema/blob/v3.2.0/CHANGELOG.rst#v320

Code diff:
python-jsonschema/jsonschema@v3.1.1...v3.2.0

Author: glarrain

requirements/base.txt

@@ -4,7 +4,7 @@
 # Required packages:
 cryptography==2.9
 defusedxml==0.6.0
-jsonschema==3.1.1
+jsonschema==3.2.0
 lxml==4.5.0
 marshmallow==2.19.5
 pyOpenSSL==18.0.0
@@ -17,12 +17,12 @@ signxml==2.6.0
 #           - pycparser
 #       - six
 #   - jsonschema
-#       - setuptools
-#       - six
 #       - attrs
-#       - importlib-metadata
+#       - importlib-metadata (python_version<'3.8')
 #           - zipp
 #       - pyrsistent
+#       - setuptools
+#       - six
 #   - signxml:
 #       - asn1crypto
 #       - certifi
@@ -39,7 +39,7 @@ certifi==2020.4.5.1
 cffi==1.14.0
 eight==0.4.2
 future==0.16.0
-importlib-metadata==1.6.0
+importlib-metadata==1.6.0; python_version<'3.8'
 pycparser==2.20
 pyrsistent==0.16.0
 # setuptools