Attempt to fix spurious build error: Remove bintray repo
Attempt to fix spurious build error: Remove bintray repo

The error observed in travis:
```
[info] Compiling 25 Scala sources and 3 Java sources to /home/travis/build/inoio/solrs/target/scala-2.11/test-classes ...
[error] error while loading <root>, Error accessing /home/travis/.coursier/cache/v1/http/jcenter.bintray.com/org/restlet/jee/org.restlet/2.3.0/org.restlet-2.3.0.jar
[error] ## Exception when compiling 28 sources to /home/travis/build/inoio/solrs/target/scala-2.11/test-classes
[error] object java.lang.Object in compiler mirror not found.
[error] scala.reflect.internal.MissingRequirementError$.signal(MissingRequirementError.scala:17)
```

inoio/solrs