downgraded checkstyle version to allow java 7 build

wumpz · wumpz · commit a9c29ffceab9 · 2019-06-19T09:29:55.000+02:00
diff --git a/pom.xml b/pom.xml
@@ -405,7 +405,7 @@
                             <dependency>
                                 <groupId>com.puppycrawl.tools</groupId>
                                 <artifactId>checkstyle</artifactId>
-                                <version>8.18</version>
+                                <version>6.19</version>
                             </dependency>
                         </dependencies>
                     </plugin>
