fix issue with single-step pages (closes usablica#229)

* Fixes issue with "Done" label not shown on pages with a single
data-step.

Signed-off-by: Adrian-Tudor Panescu <[email protected]>

Author: Adrian-Tudor Panescu

intro.js

@@ -582,11 +582,11 @@
       _placeTooltip.call(self, targetElement.element, tooltipLayer, arrowLayer);
     }
 
-    if (this._currentStep == 0) {
+    if (this._currentStep == 0 && this._introItems.length > 1) {
       prevTooltipButton.className = 'introjs-button introjs-prevbutton introjs-disabled';
       nextTooltipButton.className = 'introjs-button introjs-nextbutton';
       skipTooltipButton.innerHTML = this._options.skipLabel;
-    } else if (this._introItems.length - 1 == this._currentStep) {
+    } else if (this._introItems.length - 1 == this._currentStep || this._introItems.length == 1) {
       skipTooltipButton.innerHTML = this._options.doneLabel;
       prevTooltipButton.className = 'introjs-button introjs-prevbutton';
       nextTooltipButton.className = 'introjs-button introjs-nextbutton introjs-disabled';