Limpet failing to build under Trusty in Travis

[IanMayo]

Yesterday Travis update the build servers from Ubuntu Precise to Ubuntu Trusty.

Ubuntu Trusty doesn't have the openjdk7 we require for Limpet:

$ jdk_switcher use oraclejdk7
Switching to Oracle JDK7 (java-7-oracle), JAVA_HOME will be set to /usr/lib/jvm/java-7-oracle
update-java-alternatives: directory does not exist: /usr/lib/jvm/java-7-oracle

We have overcome by forcing the build back to precise, as described here:
https://blog.travis-ci.com/2017-07-11-trusty-as-default-linux-is-coming

But, eventually we must move to Trusty.

So, we have to find a way to compile under openjk7 under Trusty, or we have to update our build to openjk8. We can probably do this for Limpet without too much trouble.

[IanMayo]

There's a workaround here:
travis-ci/travis-ci#7964

It's to use openjdk7 instead of oraclejdk7

[IanMayo]

Ok. We introduced the workaround, but the build still fails:
https://travis-ci.org/debrief/limpet/jobs/255955145

Needs further investigation.