fix: resolves spotbugs issue (serializability of exception)

Author: simschla

lib/src/main/java/com/diffplug/spotless/npm/NpmProcessException.java

@@ -21,7 +21,7 @@
 
 public class NpmProcessException extends RuntimeException {
 	private static final long serialVersionUID = 6424331316676759525L;
-	private final ProcessRunner.Result result;
+	private final transient ProcessRunner.Result result;
 
 	public NpmProcessException(String message, ProcessRunner.Result result) {
 		super(message);