Drop support for CRuby 1.9, JRuby 1.7, Rubinius. Add TruffleRuby

.travis.yml

@@ -11,11 +11,9 @@ rvm:
   - 2.2.10
   - 2.1.10
   - 2.0.0
-  - 1.9.3
 
   - jruby-9.1.17.0
   - jruby-9.0.5.0
-  - jruby-1.7.27
 
   - ruby-head
   - ruby-2.6.0-preview2
@@ -41,7 +39,6 @@ matrix:
   allow_failures:
     - rvm: ruby-head
     - rvm: jruby-head
-    - rvm: 1.9.3
     - rvm: rbx-3
     - rvm: ruby-2.6.0-preview2
 

README.md

@@ -138,10 +138,13 @@ be obeyed though. Features developed in `concurrent-ruby-edge` are expected to m
 
 ## Supported Ruby versions
 
-MRI 1.9.3, 2.0 and above, JRuby 1.7x in 1.9 mode, JRuby 9000, and Rubinius 2.x are supported.
-This gem should be fully compatible with any interpreter that is compliant with Ruby 1.9.3 or newer.
+MRI 2.0 and above, JRuby 9000, TruffleRuby are supported. 
+This gem should be fully compatible with any interpreter that is compliant with Ruby 2.0 or newer.
 Java 8 is preferred for JRuby but every Java version on which JRuby 9000 runs is supported.
 
+Legacy support for Rubinius is kept but is no longer maintained, if you would like to help 
+please respond to [#739](https://github.com/ruby-concurrency/concurrent-ruby/issues/739)
+
 ## Usage
 
 Everything within this gem can be loaded simply by requiring it: