Fixed rubygem installation when running in yupdate script

[lslezak]

Problem

• Installation via the yupdate script failed
• The reason is that we cannot run git command at that point because yupdate downloads only the source tarball without the git history (the .git subdirectory)

Solution

• Check whether the .git directory exists, if not then use some fixed fake version. For patching a Live ISO system it is not important.

Testing

• Tested manually, yupdate can now patch the system without problem

[coveralls]

Pull Request Test Coverage Report for Build 5256297234

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 76.826%

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Totals
Change from base Build 5252695241:	0.0%
Covered Lines:	5626
Relevant Lines:	7080

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💛 - Coveralls