Bump rack-utf8_sanitizer from 1.3.2 to 1.7.0

Bumps [rack-utf8_sanitizer](https://github.com/whitequark/rack-utf8_sanitizer) from 1.3.2 to 1.7.0.
- [Release notes](https://github.com/whitequark/rack-utf8_sanitizer/releases)
- [Changelog](https://github.com/whitequark/rack-utf8_sanitizer/blob/master/CHANGELOG.md)
- [Commits](whitequark/rack-utf8_sanitizer@v1.3.2...v1.7.0)

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

Gemfile.lock

@@ -321,7 +321,7 @@ GEM
       rack (>= 1.0)
     rack-throttle (0.3.0)
       rack (>= 1.0.0)
-    rack-utf8_sanitizer (1.3.2)
+    rack-utf8_sanitizer (1.7.0)
       rack (>= 1.0, < 3.0)
     rails (4.2.11.1)
       actionmailer (= 4.2.11.1)