modify docs and composer.json to change minimum supported version of php to 5.4

Author: streamtw

composer.json

@@ -23,7 +23,7 @@
     }
   ],
   "require": {
-    "php": ">=5.5.0",
+    "php": ">=5.4.0",
     "illuminate/support": ">=4.2.0",
     "intervention/image": "2.*"
   },

doc/installation.md

@@ -39,6 +39,9 @@
         'Image' => Intervention\Image\Facades\Image::class,
     ```
 
+    Code above is for Laravel 5.1.
+    In Laravel 5.0 should leave only quoted class names.
+
 1. Publish the package's config and assets :
 
     ```bash