speed up Travis builds using caching feature

[SethTisue]

No description provided.

[SethTisue]

oops, a second run still gives:

change detected (content changed, file is created, or file is deleted):
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/bundles/scala-xml_2.11.jar
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/bundles/scala-xml_2.11.jar.md5
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/bundles/scala-xml_2.11.jar.sha1
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/docs/scala-xml_2.11-javadoc.jar
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/docs/scala-xml_2.11-javadoc.jar.md5
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/docs/scala-xml_2.11-javadoc.jar.sha1
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/ivys/ivy.xml
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/ivys/ivy.xml.md5
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_2.11/1.0.6-SNAPSHOT/ivys/ivy.xml.sha1
/home/travis/.ivy2/local/org.scala-lang.modules/scala-xm

I'll fix...

[SethTisue]

all good now, I think

👍

looks like this cuts the build time from almost 4 minutes to about 2 minutes.

[SethTisue]

I'll take the thumbs-ups and the lack of other feedback as sufficient goahead to merge.

[ashawley]

Indeed. I rebased a bunch of PRs, and it's a lot faster.

https://travis-ci.org/scala/scala-xml/pull_requests

[gourlaysama]

Awesome! 👍
I shamelessly did the same over at scala/scala-parser-combinators#100.