export.js: Retrieve the right sequence for N2

A typo (a misplaced ]) gave an undefined value which JS didn't complain about.
Therefore for N2, the sequence was retrieved until the end (thus including the J).

browser/js/export.js

@@ -570,7 +570,7 @@ Report.prototype = {
             if (this.m.clone(cloneID).getGene("4") != "undefined D"){
                 var seqN1 = seq.substring(seg['5']['stop'] + 1, seg['4']['start'])
                 var seqD = seq.substring(seg['4']['start'] , seg['4']['stop'] + 1)
-                var seqN2 = seq.substring(seg['4']['stop'] + 1, seg['3'['start']])
+                var seqN2 = seq.substring(seg['4']['stop'] + 1, seg['3']['start'])
                 $('<span/>', {'class': 'n_gene', 'text': seqN1}).appendTo(sequence);
                 $('<span/>', {'class': 'd_gene', 'text': seqD}).appendTo(sequence);
                 $('<span/>', {'class': 'n_gene', 'text': seqN2}).appendTo(sequence);