Revert "upgrade maven-compiler-plugin to 3.10.1"

This reverts commit a61ca29a.

pom.xml

@@ -36,7 +36,7 @@
       <plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-compiler-plugin</artifactId>
-        <version>3.10.1</version>
+        <version>3.2</version>
 				<configuration>
 					<source>1.7</source>
 					<target>1.7</target>