Bump mail from 2.5.3 to 2.5.5

Bumps [mail](https://github.com/mikel/mail) from 2.5.3 to 2.5.5.
- [Release notes](https://github.com/mikel/mail/releases)
- [Changelog](https://github.com/mikel/mail/blob/2.5.5/CHANGELOG.rdoc)
- [Commits](mikel/mail@2.5.3...2.5.5)

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

Author: dependabot[bot]

Gemfile.lock

@@ -94,11 +94,10 @@ GEM
       railties (>= 3.0, < 5.0)
       thor (>= 0.14, < 2.0)
     json (1.7.7)
-    mail (2.5.3)
-      i18n (>= 0.4.0)
+    mail (2.5.5)
       mime-types (~> 1.16)
       treetop (~> 1.4.8)
-    mime-types (1.22)
+    mime-types (1.25.1)
     mini_portile2 (2.4.0)
     multi_json (1.7.2)
     nokogiri (1.10.8)
@@ -107,7 +106,7 @@ GEM
       mini_portile2 (~> 2.4.0)
     pg (0.15.0)
     pg (0.15.0-x86-mingw32)
-    polyglot (0.3.3)
+    polyglot (0.3.5)
     rack (1.4.5)
     rack-cache (1.2)
       rack (>= 0.4)
@@ -164,7 +163,7 @@ GEM
     sqlite3 (1.3.7-x86-mingw32)
     thor (0.18.1)
     tilt (1.3.6)
-    treetop (1.4.12)
+    treetop (1.4.15)
       polyglot
       polyglot (>= 0.3.1)
     tzinfo (0.3.37)