Releasing version 2.1.0.

Author: evolve75

rubytree.gemspec

@@ -84,6 +84,9 @@ Gem::Specification.new do |s|
                     Thank you for installing RubyTree.
 
     Note::
+    - 2.1.0 is a minor update that brings all libraries to their
+            latest stable versions. This version no longer supports
+            Ruby 2.6 (minimum requirement is now >= 2.7).
 
     - 2.0.0 is a major release with BREAKING API changes.
             See `API-CHANGES.md` for details.