Fix Checkstyle violation

Regression introduced in fef17b0.

src/main/java/org/gaul/s3proxy/nio2blob/AbstractNio2BlobStore.java

@@ -128,7 +128,7 @@ protected AbstractNio2BlobStore(BlobStoreContext context, BlobUtils blobUtils,
         this.root = root;
     }
 
-    protected Path getRoot() {
+    protected final Path getRoot() {
         return root;
     }