Missing sys import.

```
root@c1f18c11022f:/rosette/text-embeddings-sample# python cosine_similarity.py 
Traceback (most recent call last):
  File "cosine_similarity.py", line 48, in <module>
    compare(*queries)
  File "cosine_similarity.py", line 42, in get_queries
    for line in sys.stdin:
NameError: global name 'sys' is not defined
```
Can be fixed with `import sys` at the top of the file.