Use node pattern generic parameters to simplify cop

#804 (comment)
Support introduced in rubocop/rubocop-ast#31
Presumably this will land in RuboCop 1.0 or 1.0.1 worst case.

Author: pirj

lib/rubocop/cop/rspec/multiple_expectations.rb

@@ -50,17 +50,13 @@ class MultipleExpectations < Cop
 
         MSG = 'Example has too many expectations [%<total>d/%<max>d].'
 
-        def_node_matcher :aggregate_failures?, <<-PATTERN
-          (block {
-              (send _ _ <(sym :aggregate_failures) ...>)
-              (send _ _ ... (hash <(pair (sym :aggregate_failures) true) ...>))
-            } ...)
-        PATTERN
+        ANYTHING = ->(_node) { true }
+        TRUE = ->(node) { node.true_type? }
 
-        def_node_matcher :aggregate_failures_present?, <<-PATTERN
+        def_node_matcher :aggregate_failures?, <<-PATTERN
           (block {
               (send _ _ <(sym :aggregate_failures) ...>)
-              (send _ _ ... (hash <(pair (sym :aggregate_failures) _) ...>))
+              (send _ _ ... (hash <(pair (sym :aggregate_failures) %1) ...>))
             } ...)
         PATTERN
 
@@ -89,12 +85,12 @@ def example_with_aggregate_failures?(example_node)
           node_with_aggregate_failures = find_aggregate_failures(example_node)
           return false unless node_with_aggregate_failures
 
-          aggregate_failures?(node_with_aggregate_failures)
+          aggregate_failures?(node_with_aggregate_failures, TRUE)
         end
 
         def find_aggregate_failures(example_node)
           example_node.send_node.each_ancestor(:block)
-            .find { |block_node| aggregate_failures_present?(block_node) }
+            .find { |block_node| aggregate_failures?(block_node, ANYTHING) }
         end
 
         def find_expectation(node, &block)