Introduction: Fix type (Sequential -> Iterable)

The other way to fix this would be:
```diff
-    String[] names = { "Gavin", "Stef", "Tom", "Tako" };
-    String[] uppercaseNames = names.map(String.uppercased);
+    String[] names = [ "Gavin", "Stef", "Tom", "Tako" ];
+    String[] uppercaseNames = names.collect(String.uppercased);
```
But this requires the less familiar function `collect` instead of `map`; in my opinion, the `{String*}` syntax is the lesser evil.