Fix deprecation warning in tests

Using the string version of the class reference is now deprecated when
referencing middleware. This should be written as a class not as a string.

Deprecation warning that this change fixes:
```
DEPRECATION WARNING: Passing strings or symbols to the middleware
builder is deprecated, please change
them to actual class references.  For example:
  "ActionDispatch::ShowExceptions" => ActionDispatch::ShowExceptions
```

1 files changed, 1 insertions, 1 deletions

diff --git a/actionpack/test/dispatch/session/mem_cache_store_test.rb b/actionpack/test/dispatch/session/mem_cache_store_test.rb
index 6e9107ecbf..3fed9bad4f 100644
--- a/actionpack/test/dispatch/session/mem_cache_store_test.rb
+++ b/actionpack/test/dispatch/session/mem_cache_store_test.rb
@@ -192,7 +192,7 @@ class MemCacheStoreTest < ActionDispatch::IntegrationTest
 
         @app = self.class.build_app(set) do |middleware|
           middleware.use ActionDispatch::Session::MemCacheStore, :key => '_session_id', :namespace => "mem_cache_store_test:#{SecureRandom.hex(10)}"
-          middleware.delete "ActionDispatch::ShowExceptions"
+          middleware.delete ActionDispatch::ShowExceptions
         end
 
         yield