docs: BlocListener example loss a ","

[ASE55471]

Description

The third example in BlocListener class, It doesn't effect the readability for sure, But just remind.

BlocListener<BlocA, BlocAState>(
  listenWhen: (previous, current) {
    // return true/false to determine whether or not
    // to invoke listener with state
  },
  listener: (context, state) {
    // do stuff here based on BlocA's state
  } // loss a "," here
  child: Container(),
)

[tenhobi]

Hi @ASE55471, nice catch. Do you want to create a PR for that? 🙂