Apply zig fmt to exercises

exercises/18_functions.zig

@@ -19,11 +19,10 @@ const std = @import("std");
 pub fn main() void {
     // The new function deepThought() should return the number 42. See below.
     const answer: u8 = deepThought();
-    
+
     std.debug.print("Answer to the Ultimate Question: {}\n", .{answer});
 }
 
-//
 // Please define the deepThought() function below.
 //
 // We're just missing a couple things. One thing we're NOT missing is the