Normalize requires in tests

Library/Homebrew/test/test_checksum_verification.rb

@@ -1,5 +1,5 @@
 require 'testing_env'
-require 'test/testball'
+require 'testball'
 
 class ChecksumVerificationTests < Homebrew::TestCase
   def assert_checksum_good

Library/Homebrew/test/test_cmd_cleanup.rb

@@ -1,5 +1,5 @@
 require 'testing_env'
-require 'test/testball'
+require 'testball'
 require 'cmd/cleanup'
 
 class CleanupTests < Homebrew::TestCase

Library/Homebrew/test/test_formula.rb

@@ -1,5 +1,5 @@
 require 'testing_env'
-require 'test/testball'
+require 'testball'
 
 class FormulaTests < Homebrew::TestCase
   def test_formula_instantiation

Library/Homebrew/test/test_formula_install.rb

@@ -1,6 +1,6 @@
 require 'testing_env'
 require 'formula'
-require 'test/testball'
+require 'testball'
 require 'keg'
 
 

Library/Homebrew/test/test_stdlib.rb

@@ -1,5 +1,5 @@
 require 'testing_env'
-require 'test/testball'
+require 'testball'
 require 'formula'
 require 'cxxstdlib'