Bump mini_racer from 0.2.4 to 0.2.5

Bumps [mini_racer](https://github.com/discourse/mini_racer) from 0.2.4 to 0.2.5.
- [Release notes](https://github.com/discourse/mini_racer/releases)
- [Changelog](https://github.com/discourse/mini_racer/blob/master/CHANGELOG)
- [Commits](rubyjs/mini_racer@v0.2.4...v0.2.5)

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

Gemfile.lock

@@ -154,7 +154,7 @@ GEM
     jwt (2.1.0)
     leaflet-rails (1.3.1)
       rails (>= 4.2.0)
-    libv8 (6.7.288.46.1)
+    libv8 (7.3.492.27.1)
     listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
@@ -168,8 +168,8 @@ GEM
     method_source (0.9.2)
     mini_mime (1.0.1)
     mini_portile2 (2.4.0)
-    mini_racer (0.2.4)
-      libv8 (>= 6.3)
+    mini_racer (0.2.5)
+      libv8 (>= 6.9.411)
     minitest (5.11.3)
     multi_json (1.13.1)
     multi_xml (0.6.0)