Allow failures on JRuby builds

Our builds break on JRuby, even for older Overcommit versions where the
build previously passed.

Since we don't have a good sense of the size of the userbase of
Overcommit users on JRuby, I don't want spurious build failures impeding
development.

Add a note to the README requesting any stakeholders using JRuby step
forward to maintain those builds.

Author: sds

.travis.yml

@@ -12,6 +12,10 @@ rvm:
   - 2.4.0
   - jruby-9.1.2.0
 
+matrix:
+  allow_failures:
+    - rvm: jruby-9.1.2.0
+
 before_script:
   - git config --global user.email "travis@travis.ci"
   - git config --global user.name "Travis CI"

README.md

@@ -56,7 +56,7 @@ writing any Ruby code.
 This project aims to support the following Ruby runtimes on both \*nix and Windows:
 
 * MRI 2.x
-* JRuby 9+
+* JRuby 9+ (partial—seeking maintainers who actively develop on JRuby)
 
 ## Limitations