Some changes to the build matrix used for Travis CI: * Only run with the newest and oldest version of any given compiler, not all versions in between * Never run with compilers older than the default compiler shipped in that Ubuntu version * Also start running some tests with Ubuntu 16.04
Some changes to the build matrix used for Travis CI:
* Only run with the newest and oldest version of any given compiler, not all versions in between
* Never run with compilers older than the default compiler shipped in that Ubuntu version
* Also start running some tests with Ubuntu 16.04

[ci skip]

google/fruit,google/fruit,google/fruit