Fix Checkstyle configuration to be compatible with CodeClimate's version

- CodeClimate now uses Checkstyle 9.2, in which 'scope' was removed for the JavadocMethod check

.checkstyle.xml

@@ -2,6 +2,12 @@
 <!DOCTYPE module PUBLIC
         "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
         "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+<!--
+ Note: Checkstyle likes to introduce breaking changes like removing support for certain properties. Since this
+ configuration is also used by CodeClimate, we should keep it in sync with the version that they use:
+ https://github.com/codeclimate/codeclimate-checkstyle/blob/master/bin/install-checkstyle.sh
+ https://docs.codeclimate.com/docs/checkstyle (currently outdated)
+-->
 
 <module name="Checker">
     <property name="charset" value="UTF-8"/>
@@ -149,7 +155,6 @@
             <property name="target" value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF, VARIABLE_DEF"/>
         </module>
         <module name="JavadocMethod">
-            <property name="scope" value="package"/>
             <property name="allowedAnnotations" value="Override, EventHandler"/>
             <property name="tokens" value="METHOD_DEF, ANNOTATION_FIELD_DEF"/> <!-- exclude CTOR_DEF -->
         </module>
@@ -159,11 +164,6 @@
             <property name="allowedAnnotations" value="Override, EventHandler"/>
             <property name="tokens" value="METHOD_DEF, ANNOTATION_FIELD_DEF"/> <!-- exclude CTOR_DEF -->
         </module>
-        <module name="JavadocMethod">
-            <property name="scope" value="private"/>
-            <property name="allowedAnnotations" value="Override, EventHandler"/>
-            <property name="tokens" value="METHOD_DEF, ANNOTATION_FIELD_DEF"/> <!-- exclude CTOR_DEF -->
-        </module>
         <module name="MissingJavadocMethod">
             <property name="scope" value="private"/>
             <property name="minLineCount" value="16"/>