Update mail_room to 0.8.0 to resolve #13357

Which includes the fix from:
https://github.com/tpitale/mail_room/pull/73

Gemfile

@@ -330,7 +330,7 @@ gem "newrelic_rpm", '~> 3.14'
 gem 'octokit', '~> 4.3.0'
-gem "mail_room", "~> 0.7"
+gem "mail_room", "~> 0.8"
 gem 'email_reply_parser', '~> 0.5.8'

Gemfile.lock

@@ -398,7 +398,7 @@ GEM
       systemu (~> 2.6.2)
     mail (2.6.4)
       mime-types (>= 1.16, < 4)
-    mail_room (0.7.0)
+    mail_room (0.8.0)
     method_source (0.8.2)
     mime-types (2.99.2)
     mimemagic (0.3.0)
@@ -899,7 +899,7 @@ DEPENDENCIES
   license_finder
   licensee (~> 8.0.0)
   loofah (~> 2.0.3)
-  mail_room (~> 0.7)
+  mail_room (~> 0.8)
   method_source (~> 0.8)
   minitest (~> 5.7.0)
   mousetrap-rails (~> 1.4.6)