Fix use of travis environment variables, to properly detect pull requests

Author: karenetheridge

dist.ini

@@ -270,7 +270,7 @@ skip = ^Moose::Meta::TypeConstraint::Union$
 [Test::ChangesHasContent]
 [Substitute]
 file = xt/release/changes_has_content.t
-code = s{^(note 'Checking Changes')}{my \$branch_name = \$ENV\{TRAVIS_BRANCH\};\nchomp\(\$branch_name = \`git rev-parse --abbrev-ref HEAD\`\) if not \$branch_name;\nlocal \$TODO = 'Changes need not have content for this release yet if this is only the master branch'\n    if \(\$branch_name \|\| ''\) eq 'master';\n\n$1}
+code = s{^(note 'Checking Changes')}{if \(\$ENV\{TRAVIS_PULL_REQUEST\} eq 'false'\) \{\n    chomp\(my \$branch_name = \(\$ENV\{TRAVIS_BRANCH\} || \`git rev-parse --abbrev-ref HEAD\`\)\);\n    \$TODO = 'Changes need not have content for this release yet if this is only the master branch'\n    if \(\$branch_name \|\| ''\) eq 'master';\n\}\n\n$1}
 
 ;[CheckPrereqsIndexed]