Updated .travis.yml to force the use of ant over gradle

- The custom install script prevents Travis' auto-detection of the build tool.
- `install: ant <target>` forces the use of ant even if a build.grade file is detected.

Author: emxsys

.travis.yml

@@ -25,6 +25,11 @@ addons:
     packages:
       - ant-optional
 
+# Custom install script to force using ant instead of gradle if travis detects a build.gradle file.
+install: 
+  # Using clean as dummy target; could install dependencies here if needed.
+  - ant clean
+  
 # Use xvfb to run tests that require a GUI and give it some time to start
 before_script:
   - "export DISPLAY=:99.0"