Unset _JAVA_OPTIONS env variable on Travis to suppress warning from JVM
Unset _JAVA_OPTIONS env variable on Travis to suppress warning from JVM

> Picked up _JAVA_OPTIONS: -Xmx2048m -Xms512m

* https://travis-ci.org/rspec/rspec-core/jobs/274481617
* https://travis-ci.org/rspec/rspec-expectations/jobs/275700473
* https://travis-ci.org/rspec/rspec-mocks/jobs/275700697
* https://travis-ci.org/rspec/rspec-support/jobs/275700691

rspec/rspec-dev,rspec/rspec-dev,rspec/rspec-dev