[*]: try to run some more tests via "travis-ci"

.travis.yml

@@ -9,35 +9,57 @@ php:
 os:
   - linux
 
+env:
+  global:
+    - setup=basic
+
 matrix:
   fast_finish: true
   allow_failures:
     - php: nightly
   include:
     - php: 5.3
-      env: extension='true'
+      env: extension=true
+    - php: 5.3
+      env: extension=false
     - php: 5.3
-      env: extension='false'
+      env: setup=lowest
+      env: extension=false
     - php: 5.4
-      env: extension='true'
+      env: extension=true
     - php: 5.4
-      env: extension='false'
+      env: extension=false
+    - php: 5.4
+      env: setup=lowest
+      env: extension=false
+    - php: 5.5
+      env: extension=true
     - php: 5.5
-      env: extension='true'
+      env: extension=false
     - php: 5.5
-      env: extension='false'
+      env: setup=lowest
+      env: extension=false
     - php: 5.6
-      env: extension='true'
+      env: extension=true
     - php: 5.6
-      env: extension='false'
+      env: extension=false
+    - php: 5.6
+      env: setup=lowest
+      env: extension=false
+    - php: 7.0
+      env: extension=true
     - php: 7.0
-      env: extension='true'
+      env: extension=false
     - php: 7.0
-      env: extension='false'
+      env: setup=lowest
+      env: extension=false
+    - php: 7.1
+      env: extension=true
     - php: 7.1
-      env: extension='true'
+      env: extension=false
     - php: 7.1
-      env: extension='false'
+      env: setup=lowest
+      env: extension=false
 
 before_script:
   - php --version
@@ -53,7 +75,8 @@ before_script:
   - wget https://scrutinizer-ci.com/ocular.phar
   - travis_retry composer self-update
   - travis_retry composer require satooshi/php-coveralls:1.0.0
-  - travis_retry composer install --no-interaction --prefer-source
+  - if [[ $setup = 'basic' ]]; then travis_retry composer install --prefer-dist --no-interaction; fi
+  - if [[ $setup = 'lowest' ]]; then travis_retry composer update --prefer-dist --no-interaction --prefer-lowest --prefer-stable; fi
   - composer dump-autoload -o
 
 script: