Fix examples

examples/greeter.sb

@@ -1,7 +1,7 @@
-main :: () {
+fn main() {
-    return greet("Garrit")
+    return greet("World")
 }
 
-greet :: (name) {
+fn greet(name) {
     return "Hello " + name
 }

examples/hello_world.sb

@@ -1,3 +1,3 @@
 fn main(n) {
-    n * 2;
+    return "Hello World"
 }