Not all code blocks are annotated with {:lang="js"}

[ameyp]

There are a lot of short code blocks in the book that haven't been annotated with {:lang="js"}. Would you like a pull request that encloses all code blocks in {:lang="js"}.... ?

[ameyp]

I've opened pull request #96 that adds these annotations (and {:lang="ruby"} for the handful of ruby blocks)