Bump jekyll-github-metadata to 2.10.0

[mlinksva]

To get development mode https testing fix for github.com links from jekyll/github-metadata#133

[mlinksva]

Tests failed with

$ gem install bundler
ERROR:  Error installing bundler:
	bundler requires RubyGems version >= 3.0.0. Try 'gem update --system' to update RubyGems itself.
The command "gem install bundler" failed and exited with 1 during .

I admit, I got this locally as well and couldn't work past it, hoped it was a local problem with my machine. Guess not.

This PR is not important, feel free to ignore, I'll retry eventually.

[parkr]

@mlinksva Hey! In the Travis configuration file, try adding “before_install: gem update —system”, and try the gem update —system command on your machine as well.

[mlinksva]

@parkr thanks, that worked.

I had tried gem update --system locally and got many instances of this while running tests:

      StandardError:
        ERROR:  Error installing bundler:
        	"bundle" from bundler conflicts with /Users/mlinksva/.rbenv/versions/2.5.3/bin/bundle

That was my "couldn't work past" above. Glad it is just a local problem! 😄