update diff algorithm

Author: Alexsey-VR

composer.json

@@ -3,7 +3,8 @@
     "description": "Diff generator",
     "type": "project",
     "require": {
-        "docopt/docopt": "^1.0.6"
+        "docopt/docopt": "^1.0.6",
+        "symfony/yaml": "*"
     },
     "require-dev": {
         "squizlabs/php_codesniffer": "^3.7",