message: added test for `displayBlanksAs` option
diff: * AUTH: Brent Ely (https://github.com/gitbrent/)
  * DESC: Common test/demo slides for all library features
  * DEPS: Loaded by `pptxgenjs-demo.js` and `nodejs-demo.js`
  -* VER.: 2.2.0
  -* BLD.: 20180617
  +* VER.: 2.3.0
  +* BLD.: 20180626
  */
  // Detect Node.js
  @@ -577,6 +577,8 @@ function genSlides_Chart(pptx) {
  arrDataLineStat.push( tmpObjGrn );
  arrDataLineStat.push( tmpObjUnk );
  }
  + // Create a gap for testing `displayBlanksAs` in line charts (2.3.0)
  + arrDataLineStat[2].values = [55, null, null, 55];
  // SLIDE 1: Bar Chart ------------------------------------------------------------------
  function slide1() {
  @@ -1156,6 +1158,7 @@ function genSlides_Chart(pptx) {
  chartColors: [ COLOR_RED, COLOR_AMB, COLOR_GRN, COLOR_UNK ],
  lineDataSymbolSize: 10,
  shadow: 'none',
  + //displayBlanksAs: 'gap', //uncomment only for test - looks broken otherwise!
  showLegend: true, legendPos: 'l'
  };
  slide.addChart( pptx.charts.LINE, arrDataLineStat, optsChartLine1 );
  