This version of Ruby was removed after the Yosemite update.
Download the contents of this repository:
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We must disable System Integrity Protection before we continue..
this will allow us to modify folders under /System.
To do this, power down the your Mac and hold CMD+R as the Mac is
powering on, this will bring you into recovery mode.
Now you're in recovery mode, you need to open up a Terminal:
Disable SIP by entering the following command:
csrutil disable
You should be presented with the following message:
Now restart your Mac by clicking the Apple logo at the top left,
then Restart. SIP should now have been disabled.
Now open up a Finder window and head to:
/System/Library/Frameworks/Ruby.framework/Versions
Copy the 2.0 folder from Ruby.framework/Versions/
downloaded from this repo to the path above.
Finally re-enable SIP by going into recovery mode and entering
csrutil enable
Done!