Update deps

Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

composer.json

@@ -3,6 +3,8 @@
     "description": "A comprehensive library for generating differences between two strings in multiple formats (unified, side by side HTML etc).",
     "type": "library",
     "license": "BSD-3-Clause",
+    "minimum-stability": "beta",
+    "prefer-stable": true,
     "authors": [
         {
             "name": "Jack Cherng",
@@ -30,7 +32,7 @@
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.15",
-        "phan/phan": "^1.0",
+        "phan/phan": "^2.0",
         "phpunit/phpunit": "^7.5 || ^8.0",
         "squizlabs/php_codesniffer": "^3.4"
     },