Change gradle build to use Launcher as main class

Main class was set to Bob so the GUI would not work

Changing main class to Launcher allows it to be the entry point of the application

build.gradle

@@ -43,11 +43,11 @@ test {
 }
 
 application {
-    mainClass.set("seedu.duke.Duke")
+    mainClass.set("bob.Launcher")
 }
 
 shadowJar {
-    archiveBaseName = "duke"
+    archiveBaseName = "bob"
     archiveClassifier = null
     dependsOn("distZip", "distTar")
 }