fix(axis): Fix adding duplicated <title> element

When <title> element is already appended, make to use them rather than appending.

Fix #1271

spec/internals/axis-spec.js

@@ -691,6 +691,21 @@ describe("AXIS", function() {
 					// check when toggling displaying data series
 					expect(() => chart.hide("data1")).to.not.throw();
 				});
+
+				it("shouldn't be addede duplicated tooltip <title> elements", done => {
+					chart.load({
+						columns: [
+							["data1", 130, 120, 150, 140]							
+						],
+						done: function() {
+							chart.$.main.selectAll(`.${CLASS.axisX} .tick text`).each(function() { 
+								expect(d3Select(this).selectAll("title").size()).to.be.equal(1);
+							});
+
+							done();
+						}
+					});
+				})
 			});
 
 			describe("rotated", () => {

src/axis/AxisRenderer.js

@@ -191,10 +191,12 @@ export default class AxisRenderer {
 				ctx.setTickLineTextPosition(lineUpdate, textUpdate);
 
 				// Append <title> for tooltip display
-				params.tickTitle && textUpdate.append && textUpdate.append("title")
-					.each(function(index) {
-						d3Select(this).text(params.tickTitle[index]);
-					});
+				if (params.tickTitle) {
+					const title = textUpdate.select("title");
+
+					(title.empty() ? textUpdate.append("title") : title)
+						.text(index => params.tickTitle[index]);
+				}
 
 				if (scale1.bandwidth) {
 					const x = scale1;