wsc get_train_examples doesn't match wsc data format

[eritain]

In jiant/jiant/tasks/lib/wsc.py, _create_examples() dies at the statement span1_idx=line["span1_index"] (line 177) with KeyError: 'span1_index' because it mismatches the structure of the JSON task data.

The statement should be span1_idx=line["target"]["span1_index"] and similarly for the next 3 statements.

To Reproduce

1. Install jiant v2 from any recent commit (where wsc.py hasn't been touched since 3bd801c)
2. I doubt this matters, but running Python version 3.8 in a recent linux on a 40 core, 80 thread skylake CPU with 384 GB of RAM and a VT100/16GB GPU.
3. In the Python REPL,

from jiant.proj.simple import runscript as run
import jiant.scripts.download_data.runscript as downloader
downloader.download_data(["wsc"], "/home/rasmussen.63/wsc-speed/tasks")
args = run.RunConfiguration(
   run_name="wsc-speed",
   exp_dir="wsc-speed",
   data_dir="wsc-speed/tasks",
   model_type="roberta-base",
   tasks="wsc",
   train_batch_size=16,
   num_train_epochs=3
)
run.run_simple(args)

Watch stderr come back to you until it stops at

Tokenizing Task 'wsc' for phases 'train,val,test'
WSCTask
  [train]: /home/rasmussen.63/wsc-speed/tasks/data/wsc/train.jsonl
  [val]: /home/rasmussen.63/wsc-speed/tasks/data/wsc/val.jsonl
  [test]: /home/rasmussen.63/wsc-speed/tasks/data/wsc/test.jsonl
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/rasmussen.63/jiant/jiant/proj/simple/runscript.py", line 148, in run_simple
    tokenize_and_cache.main(
  File "/home/rasmussen.63/jiant/jiant/proj/main/tokenize_and_cache.py", line 165, in main
    examples=task.get_train_examples(),
  File "/home/rasmussen.63/jiant/jiant/tasks/lib/wsc.py", line 160, in get_train_examples
    return self._create_examples(lines=read_json_lines(self.train_path), set_type="train")
  File "/home/rasmussen.63/jiant/jiant/tasks/lib/wsc.py", line 177, in _create_examples
    span1_idx=line["span1_index"],
KeyError: 'span1_index'

Expected behavior
WSCTask should initialize an Example from the downloaded data.