Remove travis php 5.6 and 7.0 build

Author: Jeremiah VALERIE

lib/generator/.travis.yml

@@ -29,8 +29,6 @@ script: bin/phpunit --color=always -v --debug
 jobs:
     include:
         - stage: Test
-          php: 5.6
-        - php: 7.0
         - php: 7.1
         - php: 7.1
           env: COMPOSER_UPDATE_FLAGS=--prefer-lowest