ignoring files/directories starting with Lib in the deps directory

[BariumOxide13716]

Reminder

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@mohanchen @PeizeLin
Please reject this pull request if it is unreasonable to introduce the following change:
In an earlier commit (two weeks ago) the LibComm and LibRI directories in path/to/abacus/deps are discarded. So I told the .gitignore file to ignore files/directories starting with 'Lib' in deps.

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[mohanchen]

I am not familiar with these codes, @PeizeLin could you review it?

[linpeize]

deps/LibRI and deps/LibComm have been deleted. What's the purpose of adding this ignore?

[BariumOxide13716]

deps/LibRI and deps/LibComm have been deleted. What's the purpose of adding this ignore?

I am not fully aware of the howLibRI or LibComm directories will be used in the future abacus compilation. If they, or some other files whose name starts with Lib, will be downloaded when abacus is compiled for some purpose and is to be merged to the develop branch, we may tell git to ignore these files.