Merge pull request #473 from shifujun/fix_bytecode_version

Fix bytecode compatible back to 52(JDK8)

pom.xml

@@ -151,8 +151,8 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.2</version>
         <configuration>
-          <source>11</source>
-          <target>11</target>
+          <source>1.8</source>
+          <target>1.8</target>
           <testSource>11</testSource>
           <testTarget>11</testTarget>
           <testCompilerArgument>-parameters</testCompilerArgument>