Update discordrb-webhooks gem

We previously used a forked version which relaxes the rest-client
dependency, this is not needed anymore.

Gemfile

@@ -233,7 +233,7 @@ gem 'connection_pool', '~> 2.0'
 gem 'redis-rails', '~> 5.0.2'
 
 # Discord integration
-gem 'discordrb-webhooks-blackst0ne', '~> 3.3', require: false
+gem 'discordrb-webhooks', '~> 3.4', require: false
 
 # HipChat integration
 gem 'hipchat', '~> 1.5.0'

Gemfile.lock

@@ -257,8 +257,8 @@ GEM
     diff-lcs (1.4.4)
     diff_match_patch (0.1.0)
     diffy (3.3.0)
-    discordrb-webhooks-blackst0ne (3.3.0)
-      rest-client (~> 2.0)
+    discordrb-webhooks (3.4.2)
+      rest-client (>= 2.0.0)
     docile (1.3.2)
     domain_name (0.5.20190701)
       unf (>= 0.0.5, < 1.0.0)
@@ -1335,7 +1335,7 @@ DEPENDENCIES
   devise-two-factor (~> 3.1.0)
   diff_match_patch (~> 0.1.0)
   diffy (~> 3.3)
-  discordrb-webhooks-blackst0ne (~> 3.3)
+  discordrb-webhooks (~> 3.4)
   doorkeeper (~> 5.5.0.rc2)
   doorkeeper-openid_connect (~> 1.7.5)
   ed25519 (~> 1.2)