Update rbenv & ruby-build github URLs

[keshayad]

Issue #, if available:
OS compatibility tests were failing with below error:

Step 8/35 : RUN git clone git://github.com/sstephenson/rbenv.git /root/.rbenv
--
1086 | ---> Running in 43e8b569eb85
1087 | Cloning into '/root/.rbenv'...
1088 | fatal: unable to connect to github.com:
1089 | github.com[0: 140.82.121.4]: errno=Connection timed out

Description of changes:
Updated the rbenv and ruby-build github URLs to fix the issue.

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[SukanyaHanumanthu]

LGTM