Upgrade Paperclip > 5.2.1 (#6404)

Mitigation for CVE-2017-0889.

https://www.cvedetails.com/cve/CVE-2017-0889/
https://medium.com/in-the-weeds/all-about-paperclips-cve-2017-0889-server-side-request-forgery-ssrf-vulnerability-8cb2b1c96fe8

Gemfile.lock

@@ -215,7 +215,7 @@ GEM
     httplog (0.99.7)
       colorize
       rack
-    i18n (0.9.1)
+    i18n (0.9.3)
       concurrent-ruby (~> 1.0)
     i18n-tasks (0.9.19)
       activesupport (>= 4.0.2)
@@ -284,7 +284,7 @@ GEM
     mimemagic (0.3.2)
     mini_mime (1.0.0)
     mini_portile2 (2.3.0)
-    minitest (5.10.3)
+    minitest (5.11.3)
     msgpack (1.1.0)
     multi_json (1.12.2)
     net-scp (1.2.1)
@@ -307,7 +307,7 @@ GEM
       http (~> 3.0)
       nokogiri (~> 1.8)
     ox (2.8.2)
-    paperclip (5.1.0)
+    paperclip (5.2.1)
       activemodel (>= 4.2.0)
       activesupport (>= 4.2.0)
       cocaine (~> 0.5.5)