spec: fix selinimum capture finalization

in aws-sdk v2, this `.read` doesn't take a block, so the files were empty

verified manually by (re-)finalizing 42613b97

Change-Id: I07fecc2fba31b46de891a000ab16c298cf9a9cc1
Reviewed-on: https://gerrit.instructure.com/99250
Reviewed-by: Jon Jensen <jon@instructure.com>
Product-Review: Jon Jensen <jon@instructure.com>
QA-Review: Jon Jensen <jon@instructure.com>
Tested-by: Jenkins
Reviewed-by: Landon Wilkins <lwilkins@instructure.com>

gems/selinimum/lib/selinimum/stat_store.rb

@@ -67,7 +67,7 @@ module Selinimum
         objects.each do |object|
           file_name = object.key.sub(prefix, "")
           File.open("#{dest}/#{file_name}", "wb") do |file|
-            object.get.body.read do |chunk|
+            object.get do |chunk|
               file.write(chunk)
             end
           end