Fix the way to handle a naughty value for scala option

 - call to shell.export_line should work in scala-build
 - see also https://github.com/travis-ci/travis-worker/blob/master/lib/travis/worker/shell/helpers.rb

.travis.yml

@@ -1,5 +1,5 @@
 language: scala
-scala: 'version defined in project/AkkaBuild.scala'
+scala: "'version defined in project/AkkaBuild.scala'"
 script: sbt test
 #  - sbt compile
 #  - sbt ";project akka-actor;test;project akka-testkit;test;project akka-actor-tests;test;project akka-remote;test;project akka-camel;test;project akka-cluster;test;project akka-slf4j;test;project akka-agent;test;project akka-transactor;test;project akka-durable-mailboxes;test;project akka-zeromq;test;project akka-docs;test"