chore(deps): pin ipython to v7.17.0 for samples, python >= 3.7 (#208)

Co-authored-by: Tres Seaver <[email protected]>
Co-authored-by: Takashi Matsuo <[email protected]>

Author: 3 people

samples/snippets/requirements.txt

@@ -1,5 +1,6 @@
 google-cloud-bigquery[pandas,bqstorage,pyarrow]==1.26.1
 google-auth-oauthlib==0.4.1
-ipython==7.16.1
+ipython==7.16.1; python_version < '3.7'
+ipython==7.17.0; python_version >= '3.7'
 matplotlib==3.3.0
 pytz==2020.1