Use Ruby 2.5.3 to generate documentation

There is a bug between Ruby 2.4 and RDoc.

Author: rafaelfranca

README.md

@@ -4,9 +4,9 @@
 
 * RVM
 
-* `rvm install 2.4.4`
+* `rvm install 2.5.3`
 
-* `rvm use 2.4.4 do gem install bundler -v 1.16.1 --no-rdoc --no-ri`
+* `rvm use 2.5.3 do gem install bundler -v 1.16.1 --no-rdoc --no-ri`
 
 * `kindlegen` must be in `PATH` ([download](http://www.amazon.com/gp/feature.html?docId=1000765211)))
 

lib/generators/config/master.rb

@@ -2,7 +2,7 @@ module Generators
   module Config
     module Master
       def ruby_version
-        '2.4.4'
+        '2.5.3'
       end
 
       def bundler_version

lib/generators/config/release.rb

@@ -7,7 +7,7 @@ module Release
       # New Rails releases should not need this project to be updated, unless new
       # unavoidable breaking dependencies need to be configured.
       def ruby_version
-        '2.4.4'
+        '2.5.3'
       end
 
       # Always use inequalities and leave an else clause to be forward compatible.