Chore: Update public_activity gem

Incorporate the latest changes to the public_activity gem:

 - https://github.com/public-activity/public_activity/releases

Refs: #4366

Gemfile

@@ -17,7 +17,7 @@ gem "textacular", "~> 5.1"
 
 gem "pdf-forms", "~> 1.2"
 
-gem "public_activity", "~> 1.6"
+gem "public_activity", "~> 2.0"
 gem "paranoia", "~> 2.4"
 gem "counter_culture", "~> 1.12"
 gem "pundit", "~> 2.0"

Gemfile.lock

@@ -349,11 +349,11 @@ GEM
     progress_bar (1.3.3)
       highline (>= 1.6, < 3)
       options (~> 2.3.0)
-    public_activity (1.6.4)
-      actionpack (>= 3.0.0)
-      activerecord (>= 3.0)
+    public_activity (2.0.2)
+      actionpack (>= 5.0.0)
+      activerecord (>= 5.0)
       i18n (>= 0.5.0)
-      railties (>= 3.0.0)
+      railties (>= 5.0.0)
     public_suffix (5.0.3)
     puma (5.6.7)
       nio4r (~> 2.0)
@@ -615,7 +615,7 @@ DEPENDENCIES
   pg (~> 1.2)
   pp_sql (~> 0.2)
   premailer-rails (~> 1.10)
-  public_activity (~> 1.6)
+  public_activity (~> 2.0)
   puma (~> 5.6.0)
   pundit (~> 2.0)
   rack-rewrite (~> 1.5)