fix dependency versions

Author: mishaschwartz

requirements.txt

@@ -27,7 +27,8 @@ gunicorn>=20; python_version >= "3"
 humanize
 jsonschema<4; python_version < "3.6"
 jsonschema>=4; python_version >= "3.6"
-jwcrypto==1.5.6; python_version >= "3.6"
+jwcrypto==1.5.6; python_version >= "3.8"
+jwcrypto==1.5.1; python_version < "3.8" and python_version >="3.6"
 jwcrypto==0.8; python_version < "3.6"  # pyup: ignore
 lxml>=3.7
 mako  # controlled by pyramid_mako