bump nim-graphql from 0.2.10 to 0.2.12

- enhancements:
  - response stream reform:
    - allow for more response stream implementation easily

- features:
  - add NodeRespStream:
    - return AST produced by execution engine instead of serialize
      it into json or something else

  - add store flag to parseSchema and parseQuery family:
    - with this additional flag, both query and schema can be marked
      with stored flag
    - purge also become selective when purging queries
    - dog fooding the introspection schema loader using this flag

bugfixes:
  - next fields will continue execution if there is error:
    - if one field failed, it will not terminate subsequent fields
      execution, but errors are kept.
  - propagate inner field error to it's parent
    - Since Non-Null type fields cannot be null, field errors are propagated to be
      handled by the parent field. If the parent field may be null then it resolves
      to null, otherwise if it is a Non-Null type, the field error is further
      propagated to it’s parent field.

    - If a List type wraps a Non-Null type, and one of the elements of that list
      resolves to null, then the entire list must resolve to null. If the List type
      is also wrapped in a Non-Null, the field error continues to propagate upwards.

    - If all fields from the root of the request to the source of the field error
      return Non-Null types, then the "data" entry in the response should be null.

vendor/nim-graphql

@@ -1 +1 @@
-Subproject commit 27edf63b0d4b447bdf05f98eaac726872cda7be8
+Subproject commit 29306c96d2cdb359e4452a55be1e3d9034f4ade7