Update gutter when firstLineNumber option is changed

Author: marijnh

lib/codemirror.js

@@ -119,7 +119,7 @@ var CodeMirror = (function() {
       focus: function(){focusInput(); onFocus(); fastPoll();},
       setOption: function(option, value) {
         options[option] = value;
-        if (option == "lineNumbers" || option == "gutter") gutterChanged();
+        if (option == "lineNumbers" || option == "gutter" || option == "firstLineNumber") gutterChanged();
         else if (option == "mode" || option == "indentUnit") loadMode();
         else if (option == "readOnly" && value == "nocursor") input.blur();
         else if (option == "theme") scroller.className = scroller.className.replace(/cm-s-\w+/, "cm-s-" + value);