CI/Examples: ModuleNotFoundError: No module named '_sqlite3'
Author: sshleifer
Pull request: no

This is a common issue,  all solutions I have found to address involve recompiling python.

like [1](https://stackoverflow.com/questions/1210664/no-module-named-sqlite3) [2](https://www.virtualizationteam.com/cloud/running-vcd-cli-fail-with-the-following-error-modulenotfounderror-no-module-named-_sqlite3.html)



Full Traceback:
```
2020-07-23T00:30:23.1433578Z ==================================== ERRORS ====================================
2020-07-23T00:30:23.1435598Z ____________ ERROR collecting examples/seq2seq/test_bash_script.py _____________
2020-07-23T00:30:23.1437122Z ImportError while importing test module '/home/hf/actions-runner_transformers/_work/transformers/transformers/examples/seq2seq/test_bash_script.py'.
2020-07-23T00:30:23.1437481Z Hint: make sure your test modules/packages have valid Python names.
2020-07-23T00:30:23.1437737Z Traceback:
2020-07-23T00:30:23.1438102Z examples/seq2seq/finetune.py:21: in <module>
2020-07-23T00:30:23.1438342Z     from .utils import (
2020-07-23T00:30:23.1438573Z examples/seq2seq/utils.py:14: in <module>
2020-07-23T00:30:23.1438821Z     from rouge_score import rouge_scorer, scoring
2020-07-23T00:30:23.1439560Z .env/lib/python3.7/site-packages/rouge_score/rouge_scorer.py:41: in <module>
2020-07-23T00:30:23.1440092Z     from nltk.stem import porter
2020-07-23T00:30:23.1440789Z .env/lib/python3.7/site-packages/nltk/__init__.py:149: in <module>
2020-07-23T00:30:23.1441053Z     from nltk.translate import *
2020-07-23T00:30:23.1441694Z .env/lib/python3.7/site-packages/nltk/translate/__init__.py:23: in <module>
2020-07-23T00:30:23.1441956Z     from nltk.translate.meteor_score import meteor_score as meteor
2020-07-23T00:30:23.1442637Z .env/lib/python3.7/site-packages/nltk/translate/meteor_score.py:10: in <module>
2020-07-23T00:30:23.1442916Z     from nltk.stem.porter import PorterStemmer
2020-07-23T00:30:23.1443523Z .env/lib/python3.7/site-packages/nltk/stem/__init__.py:29: in <module>
2020-07-23T00:30:23.1443794Z     from nltk.stem.snowball import SnowballStemmer
2020-07-23T00:30:23.1444468Z .env/lib/python3.7/site-packages/nltk/stem/snowball.py:29: in <module>
2020-07-23T00:30:23.1444741Z     from nltk.corpus import stopwords
2020-07-23T00:30:23.1445379Z .env/lib/python3.7/site-packages/nltk/corpus/__init__.py:66: in <module>
2020-07-23T00:30:23.1445750Z     from nltk.corpus.reader import *
2020-07-23T00:30:23.1446438Z .env/lib/python3.7/site-packages/nltk/corpus/reader/__init__.py:105: in <module>
2020-07-23T00:30:23.1446711Z     from nltk.corpus.reader.panlex_lite import *
2020-07-23T00:30:23.1447355Z .env/lib/python3.7/site-packages/nltk/corpus/reader/panlex_lite.py:15: in <module>
2020-07-23T00:30:23.1447591Z     import sqlite3
2020-07-23T00:30:23.1447839Z /home/hf/.pyenv/versions/3.7.6/lib/python3.7/sqlite3/__init__.py:23: in <module>
2020-07-23T00:30:23.1448311Z     from sqlite3.dbapi2 import *
2020-07-23T00:30:23.1448584Z /home/hf/.pyenv/versions/3.7.6/lib/python3.7/sqlite3/dbapi2.py:27: in <module>
2020-07-23T00:30:23.1448845Z     from _sqlite3 import *
2020-07-23T00:30:23.1449485Z E   ModuleNotFoundError: No module named '_sqlite3'
2020-07-23T00:30:23.1449638Z 

```

Comments:
Very weird. Only the seq2seq examples have a dependency on nltk, which in turn has a dependency on sqlite3?

Are we pinning a recent nltk version?

We are requiring rouge_scorer, which uses nltk for stemming. There is no pinning.

@mfuntowicz fixed, thanks!