Bump rack from 2.0.7 to 2.0.8 in /source/scripts/ruby/blog/source

Bumps [rack](https://github.com/rack/rack) from 2.0.7 to 2.0.8.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.7...2.0.8)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

source/scripts/ruby/blog/source/Gemfile.lock

@@ -80,7 +80,7 @@ GEM
     nokogiri (1.10.5)
       mini_portile2 (~> 2.4.0)
     puma (3.12.2)
-    rack (2.0.7)
+    rack (2.0.8)
     rack-test (0.6.3)
       rack (>= 1.0)
     rails (5.0.7.2)