Add another test for lastColumn

spec/integration/pr/test-pr-1487.spec.js

@@ -0,0 +1,14 @@
+const ExcelJS = verquire('exceljs');
+
+describe('github issues', () => {
+  describe('pull request 1487 - lastColumn with an empty column', () => {
+    it('Reading 1904.xlsx', () => {
+      const wb = new ExcelJS.Workbook();
+      return wb.xlsx.readFile('./spec/integration/data/1904.xlsx').then(() => {
+        const ws = wb.getWorksheet('Sheet1');
+        expect(ws.lastColumn).to.equal(ws.getColumn(2));
+      });
+    });
+  });
+  // the new property is also tested in gold.spec.js
+});