Fix missing import.

Author: nedtwigg

plugin-maven/src/main/java/com/diffplug/spotless/maven/incremental/FileIndex.java

@@ -26,6 +26,7 @@
 import java.io.PrintWriter;
 import java.io.UncheckedIOException;
 import java.nio.file.Files;
+import java.nio.file.LinkOption;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.time.Instant;