ICU-20703 Cherry-pick fixes for TravisCI build failure on Java.

This cherry-picks the changes from:
 ICU-20766 Fix failing TravisCI build for ICU4J due to missing ANT.

(cherry picked from commit ca6480832ee0ebeb7fbb37020a769a521dfa5311)
diff --git a/.travis.yml b/.travis.yml
index 90080d2..2a2d53d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -25,6 +25,11 @@
 
     - name: "j"
       language: java
+      addons:
+        apt:
+          packages:
+            - ant
+            - ant-optional
       env:      BUILD=ICU4J
       before_script:
         - cd icu4j