Install django-filer with SVG support

[jrief]

Description

Since version 2.8.2 of easy-thumbnails one must explicitly install the extra dependencies for SVG. This is done by pip install easy-thumbnails[svg].

This pull request fixes this installation problem.

Related resources

SmileyChris/easy-thumbnails#597

Checklist

• I have opened this pull request against master
• I have added or modified the tests when changing logic
• I have followed the conventional commits guidelines to add meaningful information into the changelog
• I have read the contribution guidelines and I have joined #workgroup-pr-review on
  Slack to find a “pr review buddy” who is going to review my pull request.

[codecov]

Codecov Report

Merging #1305 (f8f5705) into master (7c306dc) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1305      +/-   ##
==========================================
- Coverage   72.21%   72.18%   -0.03%     
==========================================
  Files          72       72              
  Lines        3239     3236       -3     
  Branches      563      559       -4     
==========================================
- Hits         2339     2336       -3     
  Misses        734      734              
  Partials      166      166              

Impacted Files	Coverage Δ
filer/admin/views.py	64.17% <0.00%> (-1.54%)	⬇️

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