Add missing comma after :strip_color

[Shuiei]

#44 added :strip_color to the delegate list in app/models/passkit/pass.rb without a trailing comma, so the file does not parse.

ruby -c app/models/passkit/pass.rb on current main:

app/models/passkit/pass.rb:43: syntax errors found (SyntaxError)
  41 |       :sharing_prohibited,
  42 |       :strip_color
> 43 |       :suppress_strip_shine,
     |                            ^ unexpected ',', ignoring it

This adds the comma. One line, no other change. ruby -c passes after it.