Use the new build env on Travis

faster vms with more ram and cpu, much improved boot times
minor #4561 Use the new build env on Travis (joshk)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4561).

Discussion
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Use the new build env on Travis

faster vms with more ram and cpu, much improved boot times

Commits
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9d582e4 Use the new build env on Travis