test: use Keys constant

Author: javier-godoy

src/test/java/com/flowingcode/vaadin/addons/xterm/integration/ConsoleFeatureIT.java

@@ -81,7 +81,7 @@ public void testFeature() throws InterruptedException {
 
 
     // long line
-    term.sendKeys("\n");
+    term.sendKeys(Keys.ENTER);
     assertThat(term.currentLine(), is(""));
     assertThat(term.cursorPosition(), is(pos.advance(0, 1)));