Revert "Removed EOL php versions"

This reverts commit 79b6a51441.

.travis.yml

@@ -1,19 +1,14 @@
 language: php
 
 php:
-  - 7.1
+  - 5.6
+  - 7.0
   - 7.2
 
-env:
-  matrix:
-    - PREFER_LOWEST="--prefer-lowest"
-    - PREFER_LOWEST=""
-
 before_script:
-  - composer self-update $PREFER_LOWEST
+  - composer self-update
   - composer install --prefer-source --no-interaction
 
-
 script: 
 - vendor/bin/phpunit --coverage-clover=coverage.xml