fix diff_cmd in RuleSetBuilder

Author: djydewang

lib/pmdtester/builders/rule_set_builder.rb

@@ -48,7 +48,7 @@ def diff_filenames
         base = @options.base_branch
         patch = @options.patch_branch
         # We only need to support git here, since PMD's repo is using git.
-        diff_cmd = "git diff --name-only #{base}..#{patch} -- pmd/core pmd/java"
+        diff_cmd = "git diff --name-only #{base}..#{patch} -- pmd-core pmd-java"
         filenames = Cmd.execute(diff_cmd)
       end
       filenames.split("\n")
@@ -80,7 +80,7 @@ def get_rule_sets(filenames)
 
     def build_config_file(rule_sets)
       if rule_sets.empty?
-        puts NO_JAVA_RULES_CHANGED_MESSAGE
+        logger.info NO_JAVA_RULES_CHANGED_MESSAGE
         exit 0
       end