[#249] MainApp: Update version to 1.4 (se-edu#541)

The version is 1.0.

This number is outdated, as we have recently released version 1.4 of the
app.

Let’s update the version to reflect the new version of the recent
release.

src/main/java/seedu/address/MainApp.java

@@ -40,7 +40,7 @@
  */
 public class MainApp extends Application {
 
-    public static final Version VERSION = new Version(1, 0, 0, true);
+    public static final Version VERSION = new Version(1, 4, 0, true);
 
     private static final Logger logger = LogsCenter.getLogger(MainApp.class);