ScriptFinder: change warn to debug

Having this as a WARN-level log statement is overly aggressive. No
exceptions were thrown, and skipping a non-existant directory is
expected behavior, thus this statement is downgraded to DEBUG-level.

Author: hinerm

src/main/java/org/scijava/script/ScriptFinder.java

@@ -84,7 +84,7 @@ public void findScripts(final List<ScriptInfo> scripts) {
 		final HashSet<File> scriptFiles = new HashSet<File>();
 		for (final File directory : directories) {
 			if (!directory.exists()) {
-				log.warn("Ignoring non-existent scripts directory: " +
+				log.debug("Ignoring non-existent scripts directory: " +
 					directory.getAbsolutePath());
 				continue;
 			}