example worked, minor patch for compilation failure

[lidingpku]

this example worked as expected

execute build.sh, the following part

cd apache-log4j-poc
mvn clean package

encounter BUILD FAILURE

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project log4j-rce: Compilation failure: Compilation failure:
[ERROR] Source option 5 is no longer supported. Use 6 or later.
[ERROR] Target option 1.5 is no longer supported. Use 1.6 or later.
[ERROR] -> [Help 1]

check https://stackoverflow.com/questions/53034953/error-source-option-5-is-no-longer-supported-use-6-or-later-on-maven-compile
fixed compilation by adding the following code in apache-log4j-poc/pom.xml

<properties>
   <maven.compiler.source>6</maven.compiler.source>
   <maven.compiler.target>1.6</maven.compiler.target>
 </properties>

[jeffli1024]

Thanks! incorporated in README.me