Promote truffleruby to a fully supported Ruby version

.travis.yml

@@ -13,6 +13,7 @@ rvm:
   # Latest Rubies on top
   - 2.6.0
   - jruby-9.2.5.0
+  - truffleruby-1.0.0-rc10
 
   # Older versions
   - 2.5.3
@@ -37,19 +38,9 @@ matrix:
     - rvm: 2.1.10
       env: RACK_VERSION=1.4.5
 
-    # https://github.com/oracle/truffleruby/blob/master/doc/user/standalone-distribution.md#testing-truffleruby-in-travisci
-    - name: truffleruby
-      rvm: system
-      before_install:
-        - export TRUFFLERUBY_VERSION=1.0.0-rc8
-        - curl -L https://github.com/oracle/truffleruby/releases/download/vm-$TRUFFLERUBY_VERSION/truffleruby-$TRUFFLERUBY_VERSION-linux-amd64.tar.gz | tar xz
-        - export PATH="$PWD/truffleruby-$TRUFFLERUBY_VERSION-linux-amd64/bin:$PATH"
-        - gem install bundler
-
   allow_failures:
     - rvm: ruby-head
     - rvm: jruby-head
-    - name: truffleruby
 
 before_install:
   - "gem install bundler"