Add return type declaration for "equals()" method

Author: jacek.foremski

.travis.yml

@@ -1,11 +1,6 @@
 language: php
 
 php:
-  - 5.4
-  - 5.5
-  - 5.6
-  - 7.0
-  - 7.1
   - 7.2
   - 7.3
 

README.md

@@ -38,8 +38,6 @@ class Action extends Enum
 }
 ```
 
-Note the `private` keyword requires PHP 7.1 or higher, you can omit it on PHP 7.0.
-
 ## Usage
 
 ```php

composer.json

@@ -22,7 +22,7 @@
         }
     },
     "require": {
-        "php": ">=5.4",
+        "php": ">=7.2",
         "ext-json": "*"
     },
     "require-dev": {

src/Enum.php

@@ -87,7 +87,7 @@ public function __toString()
      *
      * @return bool
      */
-    final public function equals($variable = null)
+    final public function equals($variable = null): bool
     {
         return $variable instanceof self
             && $this->getValue() === $variable->getValue()