Use commandline interface in preprocess_GLUE_tasks.sh (#937)

Summary:
Just a small fix for issue https://github.com/pytorch/fairseq/issues/936 .
Pull Request resolved: https://github.com/pytorch/fairseq/pull/937

Differential Revision: D16580263

Pulled By: myleott

fbshipit-source-id: 1777e782491c63697726e95bd555892da3fed4ec

examples/roberta/preprocess_GLUE_tasks.sh

@@ -159,7 +159,7 @@ do
   for INPUT_TYPE in $(seq 0 $((INPUT_COUNT-1)))
   do
     LANG="input$INPUT_TYPE"
-    python preprocess.py \
+    fairseq-preprocess \
       --only-source \
       --trainpref "$TASK_DATA_FOLDER/processed/train.$LANG" \
       --validpref "${DEVPREF//LANG/$LANG}" \
@@ -170,7 +170,7 @@ do
   done
   if [[ "$TASK" !=  "STS-B" ]]
   then
-    python preprocess.py \
+    fairseq-preprocess \
       --only-source \
       --trainpref "$TASK_DATA_FOLDER/processed/train.label" \
       --validpref "${DEVPREF//LANG/'label'}" \