Kotlin consumes everything in embedded markdown

[Levi-Lesches]

The codeblock.json file here is supposed to catch a code block that starts with kotlin, but it actually works when the word kotlin appears anywhere in the code block, which is... really unfortunate when writing Android docs!

This fix makes it so that it only applies when the code block starts with kotlin.

To test:

• put the cursor anywhere in the hello = 1 text
• open the command palette (ctrl+shift+P)
• choose Developer Inspect Editor and Token Scopes
• check the language field in the pop-up

This should highlight as Kotlin:

```kotlin
hello = 1
```

While this should not:

```groovy 
android {
  kotlinOptions {
    hello = 1
  }
}
```

Fixes #48