Issue #129: upgrade to checkstyle 8.4

Author: romani

README.md

@@ -14,6 +14,7 @@ This plugin provides coding rules from [Checkstyle](http://checkstyle.sourceforg
 
 Checkstyle Plugin|Sonar|Checkstyle|Jdk
 -----------------|-----|----------|---
+4.4|5.6.6|8.4|1.8
 4.3|5.6.6|8.3|1.8
 4.2|5.6.6|8.2|1.8
 4.1|5.6.6|8.1|1.8

checkstyle-sonar-plugin/config/sevntu_suppressions.xml

@@ -10,6 +10,7 @@
     <suppress checks="ForbidAnnotation" files=".*[\\/]src[\\/]main[\\/]"/>
 
     <suppress checks="ForbidAnnotation" files=".*[\\/]src[\\/]test[\\/]"/>
+    <suppress checks="AvoidModifiersForTypes" files=".*[\\/]src[\\/]main[\\/]"/>
     <!-- END of legacy code -->
 
 
@@ -18,6 +19,7 @@
     <!-- till https://github.com/checkstyle/sonar-checkstyle/issues/135 -->
     <suppress checks="MultipleStringLiteralsExtended" files="CheckstylePlugin\.java"/>
 
+
     <!-- Tone down the checking for test code -->
     <suppress checks="MultipleStringLiteralsExtended" files=".*[\\/]src[\\/]test[\\/]"/>
     <suppress checks="ForbidCCommentsInMethods" files=".*[\\/]src[\\/]test[\\/]"/>

pom.xml

@@ -85,7 +85,7 @@
   </ciManagement>
 
   <properties>
-    <checkstyle.version>8.3</checkstyle.version>
+    <checkstyle.version>8.4</checkstyle.version>
     <sonar.version>5.6.6</sonar.version>
     <sonar-java.version>3.7</sonar-java.version>
     <java.version>1.8</java.version>