Use StringBuilder in BuildFilesResolver

Change-Id: I52422ae2164a1b7106e814889ed940ed91b7d1b5
Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com>
diff --git a/org.eclipse.ui.externaltools/External Tools Base/org/eclipse/ui/externaltools/internal/variables/BuildFilesResolver.java b/org.eclipse.ui.externaltools/External Tools Base/org/eclipse/ui/externaltools/internal/variables/BuildFilesResolver.java
index a3ca6a1..b0fc9bd 100644
--- a/org.eclipse.ui.externaltools/External Tools Base/org/eclipse/ui/externaltools/internal/variables/BuildFilesResolver.java
+++ b/org.eclipse.ui.externaltools/External Tools Base/org/eclipse/ui/externaltools/internal/variables/BuildFilesResolver.java
@@ -45,7 +45,7 @@
 		IResourceDelta buildDelta = ExternalToolBuilder.getBuildDelta();
 		if (buildDelta != null)
 		{
-			final StringBuffer fileList = new StringBuffer();
+			final StringBuilder fileList = new StringBuilder();
 			final Set<String> changedResources = new LinkedHashSet<>();
 
 			// Use the argument to determine which deltas to visit - if none,