Adjust JRuby in CI for greening

JRuby 9.2.9 has a bug that causes failures on Java 11, so I'm
moving it to allowed failures for now. The bug is fixed in JRuby
9.2.10 (head) and we would like jruby-head to always be green, so
I have removed it from allowed failures.

The --dev flag should help reduce startup time for all JRuby
processes.

* Remove jruby-head from allowed failures
* Temporarily move JRuby 9.2.9 on Java 11 to allowed failures
* Add --dev to speed up JRuby launches

Author: headius

.travis.yml

@@ -63,15 +63,16 @@ matrix:
 
   allow_failures:
     - rvm: ruby-head
-    - rvm: jruby-head
     - rvm: rbx-3
     - name: TruffleRuby Latest
     - name: YARD uptodate in docs
+    - name: JRuby 9.2.9.0 Latest on Java 11
 
 env:
   global:
     - JAVA_OPTS=-Xmx1024m
     - RUBYOPT=-w
+    - JRUBY_OPTS=--dev
 
 before_install:
   - gem install bundler --version 1.17.3