Fetch libicu via Travis, switch back to container-based

This is a test.  I don't understand the details of how the `bundle config
build.charlock_holmes` bit works/fails, so the intent here is to get a PR posted
for purposes of getting feedback via the full Travis machinery.

.travis.yml

@@ -1,3 +1,10 @@
+language: ruby
+sudo: false
+addons:
+  apt:
+    packages:
+    - libicu-dev
+    - libicu48
 before_install: script/travis/before_install
 rvm:
   - 2.0.0