Apply automatic excludes for all recursive target patterns

This commit broadens the set of patterns that are considered "recursive", and thus
have automatic excludes applied for `.git`, `.gradle` and `build`.

Any target starting with `**/` is now considered recursive.

Fixes diffplug#835

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/FormatExtension.java

@@ -233,7 +233,7 @@ private final FileCollection parseTargetIsExclude(Object target, boolean isExclu
 			if (isExclude) {
 				return matchedFiles;
 			}
-			if (targetString.startsWith("**/*") || targetString.startsWith("**\\*")) {
+			if (targetString.startsWith("**/") || targetString.startsWith("**\\")) {
 				List<String> excludes = new ArrayList<>();
 				// no git
 				excludes.add(".git");