Configure Travis to run tests against examples

- move example.java so we can refer to it in Gradle as a soureSet.
- Java requires public classes be contained in identically-named files.
- using latest Travis infrastructure (better, stronger, faster).
- each piece of travis config has been confirmed as minimum necessary at
  this time.
  - without JDK specified, would run with default (Java 7)
  - without TERM=dumb, travis output is unreadable.

.travis.yml

-language: bash
+language: java
+jdk:
+  - oraclejdk8
+
+# http://docs.travis-ci.com/user/migrating-from-legacy
+sudo: false
 
 script:
   - bin/fetch-configlet
   - bin/configlet .
+  - gradle --version
+  - TERM=dumb gradle check

prime-factors/build.gradle

 dependencies {
   testCompile "junit:junit:4.12"
 }
+
+// ignore; used by track maintainers.
+sourceSets { example { } }
+dependencies { testCompile sourceSets.example.output }

robot-name/build.gradle

   mavenCentral()
 }
 
+
 dependencies {
   testCompile "junit:junit:4.10"
 }
+
+// ignore; used by track maintainers.
+sourceSets { example { } }
+dependencies { testCompile sourceSets.example.output }

settings.gradle

+include 'robot-name', 'prime-factors'