Increase minimum friendsofsymfony/http-cache to ^2.6

Author: alexander-schranz

composer.json

@@ -22,7 +22,7 @@
  ],
  "require": {
  "php": "^7.2",
- "friendsofsymfony/http-cache": "^2.5.2",
+ "friendsofsymfony/http-cache": "^2.6",
  "symfony/framework-bundle": "^3.4.26 || ^4.2.7 || ^5.0",
  "symfony/http-foundation": "^3.4.26 || ^4.2.7 || ^5.0",
  "symfony/http-kernel": "^3.4.26 || ^4.2.7 || ^5.0"