[BIGTOP-3645] upgrade fedora version to 33 in gradle files

[yoda-mon]

Description of PR

Upgrade the usage example on the task description, from fedora 26, 31 to 33, the version which Bigtop 3.0 supports.

How was this patch tested?

Check by

./gradlew tasks|grep fedora-26  
./gradlew tasks|grep fedora-31
./gradlew tasks|grep fedora-33

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'BIGTOP-3638. Your PR title ...')?
• Make sure that newly added files do not have any licensing issues. When in doubt refer to https://www.apache.org/licenses/

[iwasakims]

LGTM. Thanks, @yoda-mon!