Drop PHP 5.5 compatibility and upgrade PHPUnit to v5.x

PHPUnit 4.x contains deprecated PHP functions in PHP 7.2.

Author: ArthurHoaro

.travis.yml

@@ -9,7 +9,6 @@ php:
   - 7.1
   - 7.0
   - 5.6
-  - 5.5
 install:
   - composer self-update
   - composer install --prefer-dist

composer.json

@@ -11,11 +11,11 @@
     "keywords": ["bookmark", "link", "share", "web"],
     "config": {
         "platform": {
-            "php": "5.5.38"
+            "php": "5.6.31"
         }
     },
     "require": {
-        "php": ">=5.5",
+        "php": ">=5.6",
         "shaarli/netscape-bookmark-parser": "^2.0",
         "erusev/parsedown": "1.6",
         "slim/slim": "^3.0",
@@ -24,7 +24,7 @@
     },
     "require-dev": {
         "phpmd/phpmd" : "@stable",
-        "phpunit/phpunit": "4.8.*",
+        "phpunit/phpunit": "^5.0",
         "sebastian/phpcpd": "*",
         "squizlabs/php_codesniffer": "2.*",
         "phpunit/phpcov": "*"