Bump pillow from 4.0.0 to 7.1.0 in /study_material/intro-to-tflearn

Bumps [pillow](https://github.com/python-pillow/Pillow) from 4.0.0 to 7.1.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@4.0.0...7.1.0)

Signed-off-by: dependabot[bot] <support@github.com>

study_material/intro-to-tflearn/requirements.txt

@@ -29,7 +29,7 @@ pandas==0.19.2
 pandocfilters==1.4.1
 pexpect==4.2.1
 pickleshare==0.7.4
-Pillow==4.0.0
+Pillow==7.1.0
 prompt-toolkit==1.0.14
 protobuf==3.2.0
 ptyprocess==0.5.1