fix(chart): Correct data label text prop ref

Fix on incorrect referencing on data label's text elements

Fix #780
Close #781

spec/internals/bb-spec.js

@@ -17,10 +17,17 @@ describe("Interface & initialization", () => {
 
 	it("Check for initialization", () => {
 		chart = util.generate({
+			title: {
+				text: "test"
+			},
 			data: {
 				columns: [
 					["data1", 30]
-				]
+				],
+				labels: {
+					show: true
+				},
+				type: "bar"
 			}
 		});
 		const internal = chart.internal;
@@ -41,7 +48,7 @@ describe("Interface & initialization", () => {
 	});
 
 	it("should be accessing node elements", () => {
-		const isD3Node = v => v && "node" in v || typeof v === "undefined";
+		const isD3Node = v => v && "node" in v || false;
 
 		Object.values(chart.$).forEach(v1 => {
 			const isNode = isD3Node(v1);

spec/internals/data-spec.js

@@ -559,6 +559,13 @@ describe("DATA", () => {
 					});
 				});
 			});
+
+			it("text property shouldn't be empty", () => {
+				const texts = chart.$.text.texts;
+
+				expect(texts.empty()).to.be.false;
+				expect(texts.size() > 0).to.be.true;
+			});
 		});
 
 		describe("on area chart", () => {

src/internals/ChartInternal.js

@@ -404,7 +404,7 @@ export default class ChartInternal {
 				circles: $$.mainCircle
 			},
 			text: {
-				texts: $$.texts
+				texts: $$.mainText
 			}
 		};
 	}