Remove BlockLength cop for unit tests

Author: rastating

.rubocop.yml

@@ -52,3 +52,9 @@ Lint/UnusedMethodArgument:
 Style/ClassVars:
   Enabled: false
   Description: 'There are genuine use cases for using class vars.'
+
+Metrics/BlockLength:
+  Enabled: true
+  Description: 'Some unit tests are going to be naturally long; no need to flag this up.'
+  Exclude:
+    - spec/**/*