build: fix Checkstyle encoding (#765)

- checkstyle's parameter encoding is deprecated since commit
(apache/maven-checkstyle-plugin@627fa4f).
- use inputEncoding instead of encoding

Author: leeyazhou

pom.xml

@@ -396,7 +396,7 @@
                 <configuration>
                     <configLocation>${maven.multiModuleProjectDirectory}/apm-checkstyle/checkStyle.xml</configLocation>
                     <headerLocation>${maven.multiModuleProjectDirectory}/apm-checkstyle/CHECKSTYLE_HEAD</headerLocation>
-                    <encoding>UTF-8</encoding>
+                    <inputEncoding>${project.build.sourceEncoding}</inputEncoding>
                     <consoleOutput>true</consoleOutput>
                     <includeTestSourceDirectory>true</includeTestSourceDirectory>
                     <failOnViolation>${checkstyle.fails.on.error}</failOnViolation>