Bump execjs from 2.7.0 to 2.9.1

Bumps [execjs](https://github.com/rails/execjs) from 2.7.0 to 2.9.1.
- [Release notes](https://github.com/rails/execjs/releases)
- [Commits](rails/execjs@v2.7.0...v2.9.1)

---
updated-dependencies:
- dependency-name: execjs
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile

@@ -1,7 +1,7 @@
 source "https://rubygems.org"
 
 gem "jekyll", "4.2.2" # pinned awaiting release of https://github.com/jekyll/jekyll/pull/9304
-gem "execjs", "2.7.0" # https://github.com/rails/execjs/issues/99
+gem "execjs", "2.9.1" # https://github.com/rails/execjs/issues/99
 gem "autoprefixer-rails"
 gem "webrick" # not included in jekyll directly until 4.3.0 https://github.com/jekyll/jekyll/pull/8524
 

Gemfile.lock

@@ -21,7 +21,7 @@ GEM
     ethon (0.16.0)
       ffi (>= 1.15.0)
     eventmachine (1.2.7)
-    execjs (2.7.0)
+    execjs (2.9.1)
     ffi (1.15.5)
     fiber-local (1.0.0)
     forwardable-extended (2.6.0)
@@ -117,7 +117,7 @@ PLATFORMS
 
 DEPENDENCIES
   autoprefixer-rails
-  execjs (= 2.7.0)
+  execjs (= 2.9.1)
   html-proofer (~> 5)
   jekyll (= 4.2.2)
   jekyll-feed (~> 0.15)