Update version for 2.6.2 release. (tensorflow#1937)

Update version for 2.7.0 release. (tensorflow#1936)

Update version for 2.6.1 release. (tensorflow#1933)

Update version for 2.5.3 release. (tensorflow#1932)

Update version for 2.4.4 release. (tensorflow#1931)

Update version for 2.7.0-rc1 release. (tensorflow#1927)

Merge pull request tensorflow#1924 from jay90099/cp_r2.7_20211015_120736

Update Dockerfile.devel* with py3.7 installed.

Merge pull request tensorflow#1908 from jay90099/releng_20210819_232046

Update version for 2.6.0 release.

Merge pull request tensorflow#1906 from jay90099/releng_20210819_122841

Update version for 2.5.2 release.

Merge pull request tensorflow#1905 from jay90099/releng_20210818_195325

Update version for 2.4.3 release.