Update requirements to latest version to make it compatible with latest Django release

[Naouak]

There is some breaking changes from Marshmallow 3+ that would made the library unusable on a django 3.0 project.

[codecov-io]

Codecov Report

Merging #7 into master will decrease coverage by 12.81%.
The diff coverage is 97.91%.

@@             Coverage Diff             @@
##           master       #7       +/-   ##
===========================================
- Coverage   99.11%   86.29%   -12.82%     
===========================================
  Files          10       10               
  Lines         226      270       +44     
===========================================
+ Hits          224      233        +9     
- Misses          2       37       +35     

Impacted Files	Coverage Δ
marvelous/session.py	58.82% <85.71%> (-39.40%)	⬇️
marvelous/comic.py	93.18% <100.00%> (-6.82%)	⬇️
marvelous/comics_list.py	95.83% <100.00%> (-4.17%)	⬇️
marvelous/dates.py	100.00% <100.00%> (ø)
marvelous/events.py	100.00% <100.00%> (ø)
marvelous/series.py	94.28% <100.00%> (-2.15%)	⬇️
marvelous/urls.py	95.83% <100.00%> (-4.17%)	⬇️
marvelous/sqlite_cache.py	88.23% <0.00%> (-11.77%)	⬇️
... and 3 more

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[rkuykendall]

Beautiful work, thank you! I will work to have this published today.

[rkuykendall]

Released in v1.1.1.