proto-map->clj-map doesnt convert to clj proto-maps when they are values of map

when you have a proto of this type:
```

message AAA {
}

message BBB {
}
message Msg {
  AAA aaa = 1;
  map<string, BBB> bbb = 2; 
}

when you invoke proto-map->clj-map on Msg, it will convert Msg, & the inner AAA into clj maps
but it will keep all the values of bbb as proto-maps
```