Update checkstyle from 7.6 to 8.21

AreaShop/src/main/java/me/wiefferink/areashop/features/signs/RegionSign.java

@@ -96,7 +96,7 @@ public class RegionSign {
 	}
 
 	/**
-	 * Get the material of the sign
+	 * Get the material of the sign.
 	 * @return Material of the sign, normally {@link Material#WALL_SIGN} or {@link Material#SIGN_POST}, but could be something else or null.
 	 */
 	public Material getMaterial() {

AreaShop/src/main/java/me/wiefferink/areashop/managers/FileManager.java

@@ -512,7 +512,7 @@ public class FileManager extends Manager {
 	}
 
 	/**
-	 * Update a list of regions
+	 * Update a list of regions.
 	 * @param regions The list of regions to update.
 	 */
 	public void updateRegions(List<GeneralRegion> regions) {

config/checkstyle.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE module PUBLIC
-    "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
-    "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+    "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <!--
     Based on the Google Java Style Guide: https://google.github.io/styleguide/javaguide.html
@@ -42,9 +42,7 @@
             <property name="tokens" value="LITERAL_TRY, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, LITERAL_SWITCH"/>
         </module>
         <module name="NeedBraces"/>
-        <module name="LeftCurly">
-            <property name="maxLineLength" value="100"/>
-        </module>
+        <module name="LeftCurly" />
         <module name="RightCurly">
             <property name="id" value="RightCurlySame"/>
             <property name="tokens" value="LITERAL_TRY, LITERAL_CATCH, LITERAL_FINALLY, LITERAL_DO"/>

pom.xml

@@ -68,12 +68,12 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-checkstyle-plugin</artifactId>
-        <version>2.17</version>
+        <version>3.1.0</version>
         <dependencies>
           <dependency>
             <groupId>com.puppycrawl.tools</groupId>
             <artifactId>checkstyle</artifactId>
-            <version>7.6</version>
+            <version>8.21</version>
           </dependency>
         </dependencies>
         <executions>