chore(deps-dev): bump letter_opener from 1.9.0 to 1.10.0

Bumps [letter_opener](https://github.com/ryanb/letter_opener) from 1.9.0 to 1.10.0.
- [Changelog](https://github.com/ryanb/letter_opener/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ryanb/letter_opener/compare/v1.9.0...v1.10.0)

---
updated-dependencies:
- dependency-name: letter_opener
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -207,6 +207,7 @@ GEM
       nokogiri (~> 1.10, >= 1.10.4)
       rubyzip (>= 1.3.0, < 3)
     cgi (0.3.6)
+    childprocess (5.0.0)
     choice (0.2.0)
     chronic (0.10.2)
     coderay (1.1.3)
@@ -386,10 +387,11 @@ GEM
     knapsack_pro (6.0.4)
       rake
     language_server-protocol (3.17.0.3)
-    launchy (2.5.2)
+    launchy (3.0.0)
       addressable (~> 2.8)
-    letter_opener (1.9.0)
-      launchy (>= 2.2, < 3)
+      childprocess (~> 5.0)
+    letter_opener (1.10.0)
+      launchy (>= 2.2, < 4)
     link_header (0.0.8)
     listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)