Build server only when required

scripts/install-spigot.sh

@@ -15,7 +15,7 @@ for ver in "${versions[@]}"; do
   mvn -q org.apache.maven.plugins:maven-dependency-plugin:3.9.0:get -Dartifact=org.spigotmc:spigot:${ver}-R0.1-SNAPSHOT
 
   ARTIFACT="spigot-${ver}.jar"
-  if [ "$?" -eq 0 ] && [ -e "/build/$ARTIFACT" ]; then
+  if [ "$?" -eq 0 ] && [[ "$SERVER_REQUIRED" == "false" || -e "/build/$ARTIFACT" ]]; then
     echo "Located spigot $ver successfully"
   else
     echo "Spigot $ver not located, building..."