Rename variable to fix conflicting fs name

fs is initially declared as the file system module, but in parseField() an internal unrelated variable is also named fs.

Renamed the second, internal variable from fs to _fs to fix this conflict.

lib/hl7/parser.js

@@ -80,9 +80,9 @@ parser.prototype.parseField = function(s) {
   var f = new field();
 
   if (s.indexOf(this.delimiters.repititionCharacter) != -1) {
-    var fs = s.split(this.delimiters.repititionCharacter);
-    for (var i = 0; i < fs.length; i++) {
-      f.value.push(this.parseField(fs[i]));
+    var _fs = s.split(this.delimiters.repititionCharacter);
+    for (var i = 0; i < _fs.length; i++) {
+      f.value.push(this.parseField(_fs[i]));
     }
   } else {
     var components = s.split(this.delimiters.componentSeperator);