Travis/Tox: Remove versions <2.2, Add 3.0

[tony]

Re: #46

[tony]

Once django-classy-tags is 3.0 ready this will be good to go django-cms/django-classy-tags#50

cc: @meloncafe @hellysmile

[codecov]

Codecov Report

Merging #48 into master will increase coverage by 1.09%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master    #48      +/-   ##
========================================
+ Coverage    98.9%   100%   +1.09%     
========================================
  Files           8      8              
  Lines         183    183              
========================================
+ Hits          181    183       +2     
+ Misses          2      0       -2

Impacted Files	Coverage Δ
django_activeurl/utils.py	100% <0%> (+1.78%)	⬆️

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