upgrade to laravel 7 and set branch to v2

vendor/symfony/http-kernel/RebootableInterface.php

@@ -21,10 +21,10 @@ interface RebootableInterface
     /**
      * Reboots a kernel.
      *
-     * The getCacheDir() method of a rebootable kernel should not be called
-     * while building the container. Use the %kernel.cache_dir% parameter instead.
+     * The getBuildDir() method of a rebootable kernel should not be called
+     * while building the container. Use the %kernel.build_dir% parameter instead.
      *
-     * @param string|null $warmupDir pass null to reboot in the regular cache directory
+     * @param string|null $warmupDir pass null to reboot in the regular build directory
      */
-    public function reboot($warmupDir);
+    public function reboot(?string $warmupDir);
 }