set pyasn1 required version to prevent conflict with pyasn1-modules

pyasn1-modules v0.2.1 requires pyasn1 <0.5.0, >=0.4.1 but for whatever
reason, `pip3 install` is not picking it up properly.  Perhaps because pip3
finds an older version of pyasn1 installed but does not upgrade it.

* https://github.com/etingof/pyasn1-modules/issues/10
* https://gitlab.com/eighthave/fdroidserver/-/jobs/67781548

setup.py

@@ -88,8 +88,8 @@ setup(name='fdroidserver',
           'paramiko',
           'Pillow',
           'apache-libcloud >= 0.14.1',
-          'pyasn1',
-          'pyasn1-modules',
+          'pyasn1 <0.5.0, >=0.4.1',
+          'pyasn1-modules == 0.2.1',
           'python-vagrant',
           'PyYAML',
           'qrcode',