Support relative paths in extension-installer (https://github.com/phpstan/phpstan-src/commit/0e306c66ca4c6f31184e222ce5df04a17b4307ca), https://github.com/phpstan/extension-installer/issues/17
Starting with phpstan/phpstan 0.12.62 and phpstan/extension-installer 1.1.0, relative paths to extension configs are used. This allows the generated config to be moved across filesystems, for example from a host system to a Docker container.