[dogfooding] Use String.join JDT cleanup in p2

The resulting code is much shorter.

Change-Id: I1b5e6a59b1cc236c273e8005c174ef6bdf393341
Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com>
Reviewed-on: https://git.eclipse.org/r/c/equinox/rt.equinox.p2/+/179100
Tested-by: Equinox Bot <equinox-bot@eclipse.org>
diff --git a/bundles/org.eclipse.equinox.p2.jarprocessor/src/org/eclipse/equinox/internal/p2/jarprocessor/Utils.java b/bundles/org.eclipse.equinox.p2.jarprocessor/src/org/eclipse/equinox/internal/p2/jarprocessor/Utils.java
index d9a7e9c..d24dbc3 100644
--- a/bundles/org.eclipse.equinox.p2.jarprocessor/src/org/eclipse/equinox/internal/p2/jarprocessor/Utils.java
+++ b/bundles/org.eclipse.equinox.p2.jarprocessor/src/org/eclipse/equinox/internal/p2/jarprocessor/Utils.java
@@ -290,13 +290,8 @@
 	}
 
 	public static String concat(String[] array) {
-		StringBuilder buffer = new StringBuilder();
-		for (int i = 0; i < array.length; i++) {
-			if (i > 0)
-				buffer.append(' ');
-			buffer.append(array[i]);
-		}
-		return buffer.toString();
+		String buffer = String.join(String.valueOf(' '), array);
+		return buffer;
 	}
 
 	public static String[] toStringArray(String input, String separator) {