Fixed a test I broke with overzealous find/replace.

Author: jdantonio

spec/concurrent/executor/thread_pool_executor_shared.rb

@@ -342,16 +342,16 @@
     end
   end
 
-  context '#fallback_policy' do
-    context ':caller_runs is honoured even if the old fallback_policy arg is used' do
+  context '#overflow_policy' do
+    context ':caller_runs is honoured even if the old overflow_policy arg is used' do
 
       subject do
         described_class.new(
           min_threads: 1,
           max_threads: 1,
           idletime: 60,
           max_queue: 1,
-          fallback_policy: :caller_runs
+          overflow_policy: :caller_runs
         )
       end