chore: Pin werkzeug version

[iamareebjamal]

Since we are directly depending on werkzeug, it should
be tracked in requirements file so that transitive upgrade
does not break the project

[iamareebjamal]

https://travis-ci.org/fossasia/open-event-server/builds/647520319?utm_source=github_status&utm_medium=notification

pallets/werkzeug#1714

[codecov]

Codecov Report

Merging #6824 into development will increase coverage by <.01%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development    #6824      +/-   ##
===============================================
+ Coverage        65.85%   65.86%   +<.01%     
===============================================
  Files              307      307              
  Lines            15382    15382              
===============================================
+ Hits             10130    10131       +1     
+ Misses            5252     5251       -1

Impacted Files	Coverage Δ
app/models/event.py	81.27% <0%> (+0.35%)	⬆️

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