Make ForeignExe serializable.

Author: nedtwigg

lib/src/main/java/com/diffplug/spotless/ForeignExe.java

@@ -16,6 +16,7 @@
 package com.diffplug.spotless;
 
 import java.io.IOException;
+import java.io.Serializable;
 import java.nio.charset.Charset;
 import java.util.Objects;
 import java.util.regex.Matcher;
@@ -31,7 +32,8 @@
  * Usage: {@code ForeignExe.nameAndVersion("grep", "2.5.7").confirmVersionAndGetAbsolutePath()}
  * will find grep, confirm that it is version 2.5.7, and then return.
  */
-public class ForeignExe {
+public class ForeignExe implements Serializable {
+	private static final long serialVersionUID = 1L;
 	private @Nullable String pathToExe;
 	private String versionFlag = "--version";
 	private Pattern versionRegex = Pattern.compile("version (\\S*)");