Disable some more rubocop rules

Rubocop will probably be ripped out completely in the future, but
for right now, just disable the rules that are complaining.

.rubocop.yml

@@ -28,9 +28,15 @@ Metrics/BlockLength:
     - spec/**/*
     - rack-test.gemspec
 
-# Rationale: Enforcing maximum module length makes code worse, without exception
+# Rationale: Enforcing maximum length/complexity makes code worse, without exception
 Metrics/ModuleLength:
   Enabled: false
+Metrics/ClassLength:
+  Enabled: false
+Metrics/AbcSize:
+  Enabled: false
+Metrics/PerceivedComplexity:
+  Enabled: false
 
 # Rationale: allow Weirich-style blocks, but do not enforce them.
 Style/BlockDelimiters: