Build error: values-21 should be values-v21

[geekarist]

The error is in this step:
https://codelabs.developers.google.com/codelabs/material-design-style/#6

This paragraph is wrong:

In values-21 folder, update styles.xml to create system bar transparent for device running Android 5 and above.

See this answer: http://stackoverflow.com/a/31361546.