Bump html-proofer from 3.15.3 to 3.17.2

Bumps [html-proofer](https://github.com/gjtorikian/html-proofer) from 3.15.3 to 3.17.2.
- [Release notes](https://github.com/gjtorikian/html-proofer/releases)
- [Commits](gjtorikian/html-proofer@v3.15.3...v3.17.2)

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

Gemfile.lock

@@ -13,7 +13,7 @@ GEM
     eventmachine (1.2.7)
     ffi (1.13.1)
     forwardable-extended (2.6.0)
-    html-proofer (3.15.3)
+    html-proofer (3.17.2)
       addressable (~> 2.3)
       mercenary (~> 0.3)
       nokogumbo (~> 2.0)
@@ -57,12 +57,12 @@ GEM
     mini_portile2 (2.4.0)
     nokogiri (1.10.10)
       mini_portile2 (~> 2.4.0)
-    nokogumbo (2.0.2)
+    nokogumbo (2.0.3)
       nokogiri (~> 1.8, >= 1.8.4)
-    parallel (1.19.2)
+    parallel (1.20.1)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
-    public_suffix (4.0.5)
+    public_suffix (4.0.6)
     rainbow (3.0.0)
     rb-fsevent (0.10.4)
     rb-inotify (0.10.1)