gems: re-enable meta_request.

Upstream finally released a new version that fixed the "stack level too
deep" bug on Rails 6.1.

Gemfile.lock

@@ -256,6 +256,9 @@ GEM
     marcel (1.0.1)
     memoist (0.16.2)
     memory_profiler (1.0.0)
+    meta_request (0.7.3)
+      rack-contrib (>= 1.1, < 3)
+      railties (>= 3.0.0, < 7)
     method_source (1.0.0)
     mini_mime (1.1.1)
     mini_portile2 (2.6.1)
@@ -315,6 +318,8 @@ GEM
       activesupport (>= 3.0.0)
     racc (1.5.2)
     rack (2.2.3)
+    rack-contrib (2.3.0)
+      rack (~> 2.0)
     rack-mini-profiler (2.3.3)
       rack (>= 1.2.0)
     rack-proxy (0.7.0)
@@ -513,6 +518,7 @@ DEPENDENCIES
   mail
   memoist
   memory_profiler
+  meta_request
   minitest-ci
   minitest-reporters
   mocha
@@ -558,4 +564,4 @@ DEPENDENCIES
   webpacker (= 6.0.0.beta.6)
 
 BUNDLED WITH
-   2.1.4
+   2.2.22