Upgrade redis to v4 (#561)

Author: ahangarha

Gemfile

@@ -31,7 +31,7 @@ gem "coffee-rails"
 
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
 gem "jbuilder"
-gem "redis", "3.3.3"
+gem "redis", "~> 4.0"
 
 # bundle exec rake doc:rails generates the API under doc/api.
 gem "sdoc", group: :doc

Gemfile.lock

@@ -289,7 +289,7 @@ GEM
       rails (>= 5.2)
       rainbow (~> 3.0)
     redcarpet (3.6.0)
-    redis (3.3.3)
+    redis (4.8.1)
     regexp_parser (2.8.1)
     reline (0.3.8)
       io-console (~> 0.5)
@@ -454,7 +454,7 @@ DEPENDENCIES
   rainbow
   react_on_rails (= 13.2.0)
   redcarpet
-  redis (= 3.3.3)
+  redis (~> 4.0)
   rspec-rails (~> 6.0.0)
   rubocop (= 1.24.1)
   rubocop-performance (~> 1.13)