Language module requirement: fix perl test

The name of the module is "Env", not "ENV"; this test would fail on a
case-sensitive filesystem.

Library/Homebrew/test/test_language_module_requirement.rb

@@ -32,7 +32,7 @@ class LanguageModuleRequirementTests < Homebrew::TestCase
   end
 
   def test_good_perl_deps
-    assert_deps_pass "ENV" => :perl
+    assert_deps_pass "Env" => :perl
   end
 
   def test_bad_python_deps