refactor: use '->' instead of ':' for fn return type

Author: jakbyte

resources/fibonacci.mun

@@ -1,11 +1,11 @@
-fn nth(): int {
+fn nth() -> int {
     3
 }
 
-fn fibonacci(n:int):int {
+fn fibonacci(n: int) -> int {
     if n <= 1 {
         n
     } else {
-        fibonacci(n-1) + fibonacci(n-2)
+        fibonacci(n - 1) + fibonacci(n - 2)
     }
 }