Switched Travis to test against 4.1

.travis.yml

@@ -6,14 +6,16 @@ php:
   - 7.1
 
 env:
-  - DB=MYSQL CORE_RELEASE=4.0
+  - DB=MYSQL CORE_RELEASE=4.1
 
 matrix:
   include:
     - php: 7.1
-      env: DB=PGSQL CORE_RELEASE=4.0
+      env: DB=PGSQL CORE_RELEASE=4.1
     - php: 7.1
-      env: DB=SQLITE3 CORE_RELEASE=4.0
+      env: DB=SQLITE3 CORE_RELEASE=4.1
+    - php: 5.6
+      env: DB=MYSQL CORE_RELEASE=4.0
 
 before_script:
   # Init PHP
@@ -30,4 +32,4 @@ before_script:
   - composer install --prefer-dist --no-interaction --no-progress --no-suggest --optimize-autoloader --verbose --profile
 
 script:
-  - vendor/bin/phpunit
+  - vendor/bin/phpunit