Bump version to 2.4

[penghuo]

Signed-off-by: Peng Huo penghuo@gmail.com

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov-commenter]

Codecov Report

Merging #832 (dcff20d) into 2.x (7bb52a8) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                2.x     #832   +/-   ##
=========================================
  Coverage     94.83%   94.83%           
  Complexity     2916     2916           
=========================================
  Files           291      291           
  Lines          7795     7795           
  Branches        567      567           
=========================================
  Hits           7392     7392           
  Misses          349      349           
  Partials         54       54           

Flag	Coverage Δ
query-workbench	62.76% <ø> (ø)
sql-engine	97.78% <ø> (ø)

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