Stop running Java 7 tests on Travis CI
Stop running Java 7 tests on Travis CI

Multiple reasons:

* Java 7 only works, somewhat (see below), in the precise environment. The precise build environment is deprecated by Tracis CI
* Java 7 went EoL in 2015
* I did, unsuccessful, attempts to get green Java 7 builds in #37 and #39

Close #38

twingly/twingly-search-api-java,twingly/twingly-analytics-api-java