[BEAM-1580] Fixed typos in the Python SDK examples. ( tornatoes -> tornadoes )

[sungjunyoung]

• Make sure the PR title is formatted like:
  [BEAM-<Jira issue #>] Description of pull request
• Make sure tests pass via mvn clean verify. (Even better, enable
  Travis-CI on your fork and ensure the whole test matrix passes).
• Replace <Jira issue #> in the title with the actual Jira issue
  number, if there is one.
• If this contribution is large, please file an Apache
  Individual Contributor License Agreement.

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[coveralls]

Coverage increased (+28.0%) to 98.318% when pulling 1b59e33 on sungjunyoung:master into 935ecd4 on apache:master.

[asfbot]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/beam_PreCommit_Java_MavenInstall/8996/

Failed Tests: 1

beam_PreCommit_Java_MavenInstall/org.apache.beam:beam-examples-java: 1

• org.apache.beam.examples.WindowedWordCountIT.testWindowedWordCountInStreaming

--none--

[sb2nov]

LGTM

R: @aaltay PTAL

[aaltay]

Thank you @sungjunyoung!