Change return type of next_bool(random) from void to bool

lib/std/math/math_random.c3

@@ -48,7 +48,7 @@ fn int rand(int max) @builtin
 /**
  * @require is_random(random)
  **/
-macro void next_bool(random)
+macro bool next_bool(random)
 {
 	return random.next_byte() & 1;
 }
@@ -94,4 +94,4 @@ macro @random_value_to_bytes(#function, char[] bytes)
 		bytes = bytes[$byte_size..];
 	}
 	unreachable();
-}
+}