Bump letter_opener_web from 1.4.0 to 2.0.0

Bumps [letter_opener_web](https://github.com/fgrehm/letter_opener_web) from 1.4.0 to 2.0.0.
- [Release notes](https://github.com/fgrehm/letter_opener_web/releases)
- [Changelog](https://github.com/fgrehm/letter_opener_web/blob/master/CHANGELOG.md)
- [Commits](https://github.com/fgrehm/letter_opener_web/compare/v1.4.0...v2.0.0)

---
updated-dependencies:
- dependency-name: letter_opener_web
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Gemfile.lock

@@ -362,12 +362,13 @@ GEM
       kramdown (~> 2.0)
     launchy (2.5.0)
       addressable (~> 2.7)
-    letter_opener (1.7.0)
-      launchy (~> 2.2)
-    letter_opener_web (1.4.0)
-      actionmailer (>= 3.2)
-      letter_opener (~> 1.0)
-      railties (>= 3.2)
+    letter_opener (1.8.1)
+      launchy (>= 2.2, < 3)
+    letter_opener_web (2.0.0)
+      actionmailer (>= 5.2)
+      letter_opener (~> 1.7)
+      railties (>= 5.2)
+      rexml
     loofah (2.18.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
@@ -753,7 +754,7 @@ DEPENDENCIES
   kaminari (~> 1.2.2)
   knapsack_pro (~> 3.3.1)
   launchy (~> 2.5.0)
-  letter_opener_web (~> 1.4.0)
+  letter_opener_web (~> 2.0.0)
   mdl (~> 0.11.0)
   mini_magick (~> 4.11.0)
   omniauth (~> 2.0.4)