changed namedField "ARC-Compressed-Offset" to "ARC-Gzip-Offset" for even more clarity

commons/src/main/java/org/archive/io/Arc2Warc.java

@@ -155,7 +155,7 @@ throws IOException {
            r.getHeaderString());
        ar.addLabelValue("ARC-File", 
            r.getMetaData().getArc());
-       ar.addLabelValue("ARC-Compressed-Offset", 
+       ar.addLabelValue("ARC-Gzip-Offset", 
            String.valueOf(r.getHeader().getOffset()));
        ar.addLabelValue("ARC-Length", 
            String.valueOf(r.getHeader().getLength()));