Update git submodules to use relative paths

[sayomaki]

As mentioned in the discussion group, ssh users who clones the js-slang repo may face issues when checking out submodules (i.e. py-slang and scm-slang) if their https credentials are not yet properly set up. Thus, to better cater to both demographics (users cloning via the https:// protocol and users cloning via the ssh:// protocol), it would be better to use relative paths instead.

The reason why the relative path is set to traverse 2 level up (and then back with the source-academy prefix) is so that user forks will not be affected (as only going 1 level up will result in git trying to find a fork of the two repos py-slang and scm-slang under users' own account, which may or may not exist, and could be not the most updated version either).

[coveralls]

Pull Request Test Coverage Report for Build 8657038476

Details

• 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 81.971%

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Totals
Change from base Build 8657000059:	0.0%
Covered Lines:	10767
Relevant Lines:	12788

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💛 - Coveralls