[MINOR] Fixed checkstyle config to be based off Maven root-dir (requires Maven >=3.3.1 to work properly); (#4009)

Updated README

README.md

@@ -51,7 +51,7 @@ Prerequisites for building Apache Hudi:
 * Unix-like system (like Linux, Mac OS X)
 * Java 8 (Java 9 or 10 may work)
 * Git
-* Maven
+* Maven (>=3.3.1)
 
 ```
 # Checkout code and build

pom.xml

@@ -231,6 +231,8 @@
           <sourceDirectories>
             <sourceDirectory>${project.build.sourceDirectory}</sourceDirectory>
           </sourceDirectories>
+          <!-- NOTE: This property is only available in Maven >= 3.3.1 -->
+          <propertyExpansion>basedir=${maven.multiModuleProjectDirectory}</propertyExpansion>
           <excludes>**\/generated-sources\/</excludes>
         </configuration>
         <executions>

style/checkstyle.xml

@@ -305,7 +305,7 @@
         <module name="SimplifyBooleanExpression"/>
 
         <module name="ImportControl">
-            <property name="file" value="style/import-control.xml"/>
+            <property name="file" value="${basedir}/style/import-control.xml"/>
             <property name="path" value="^.*[\\/]hudi-client[\\/]hudi-client-common[\\/]src[\\/].*$"/>
         </module>