Fix depreciated 'buildDir'

Author: purejava

build.gradle

@@ -113,7 +113,7 @@ githubRelease {
     setBody("[![Downloads](https://img.shields.io/github/downloads/purejava/keepassxc-cryptomator/latest/keepassxc-cryptomator-${project.version}.jar)](https://github.com/purejava/keepassxc-cryptomator/releases/latest/download/keepassxc-cryptomator-${project.version}.jar)\n" +
             "\n" +
             "- xxx")
-    releaseAssets = fileTree(dir: "${buildDir}/libs", includes: [
+    releaseAssets = fileTree(dir: "${layout.buildDirectory}/libs", includes: [
             "keepassxc-cryptomator-${version}.jar",
             "keepassxc-cryptomator-${version}.jar.asc",
             "keepassxc-cryptomator-${version}-sources.jar",