Remove unsupported php7 runtime from .travis.yml

Author: Eugene Leonovich

.travis.yml

@@ -9,7 +9,6 @@ env:
   - PHP_RUNTIME='php:5.4-cli'
   - PHP_RUNTIME='php:5.5-cli'
   - PHP_RUNTIME='php:5.6-cli' PHPUNIT_OPTS='--coverage-clover coverage.clover'
-  - PHP_RUNTIME='php:7.0-cli'
 
 before_install:
   # https://github.com/travis-ci/travis-ci/issues/4778