README.md in cureutils-1.5.0 vs README.md in cureutils-1.6.0

@@ -13,21 +13,18 @@
 </p>
 
 
 ## Requirements
 
-* ruby >= 2.2.2
+* ruby >= 2.6
   + more: [.travis.yml](./.travis.yml)
 
 ## Installation
 
 Install:
 
 ```
 $ gem install cureutils
-
-# for 2.2
-$ gem install 'backport_dig'
 ```
 
 
 After that, `cure` command is available.