UPGRADE_GUIDE.md in volt-0.9.3.pre3

- old
+ new

@@ -9,6 +9,8 @@
 gem 'rbnacl-libsodium', require: false
 
 # Asset compilation gems, they will be required when needed.
 gem 'csso-rails', '~> 0.3.4', require: false
 gem 'uglifier', '>= 2.4.0', require: false
+
+gem 'volt-mongo'
 ```
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