Add RGBA functionnality to Color Provider

Author: apsylone

src/Faker/Provider/Color.php

@@ -90,6 +90,14 @@ public static function rgbCssColor()
         return 'rgb(' . static::rgbColor() . ')';
     }
 
+    /**
+     * @example 'rgba(0,255,122,0.8)'
+     */
+    public static function rgbaCssColor()
+    {
+        return 'rgba(' . static::rgbColor() . ',' . static::randomFloat(1, 0, 1) . ')';
+    }
+
     /**
      * @example 'blue'
      */