Rename PMD ruleset, update PMD.

Codacy looks for ruleset.xml, so give it what it wants.
Bump PMD version to the one used by Codacy, for consistency.

gradle/analysis.gradle

@@ -26,14 +26,14 @@ configurations {
 dependencies {
     codacy 'com.codacy:codacy-coverage-reporter:1.0.13'
 
-    pmd group: 'net.sourceforge.pmd', name: 'pmd-core', version: '5.2.3'
-    pmd group: 'net.sourceforge.pmd', name: 'pmd-java', version: '5.2.3'
+    pmd group: 'net.sourceforge.pmd', name: 'pmd-core', version: '5.5.2'
+    pmd group: 'net.sourceforge.pmd', name: 'pmd-java', version: '5.5.2'
 }
 
 pmd {
     ruleSets = []
-    ruleSetFiles = files("$rootDir/etc/pmd/full.xml")
-    toolVersion = '5.2.3'
+    ruleSetFiles = files("$rootDir/etc/pmd/ruleset.xml")
+    toolVersion = '5.5.2'
     ignoreFailures = true
 }