Polish java version setting.

pom.xml

@@ -7,7 +7,8 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
-        <java.version>1.8</java.version>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
         <spring-version>4.0.0.RELEASE</spring-version>
     </properties>
     <artifactId>webmagic-parent</artifactId>
@@ -223,10 +224,6 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
-                <configuration>
-                    <source>${java.version}</source>
-                    <target>${java.version}</target>
-                </configuration>
             </plugin>
             <!--<plugin>-->
                 <!--<groupId>org.apache.maven.plugins</groupId>-->