maven指定JDK版本

<profile>
	<id>jdk-1.7</id>
	<activation>
		<activeByDefault>true</activeByDefault>
		<jdk>1.7</jdk>
	</activation>
	<properties>
		<maven.compiler.source>1.7</maven.compiler.source>
		<maven.compiler.target>1.7</maven.compiler.target>
		<maven.compiler.compilerVersion>1.7</maven.compiler.compilerVersion>
	</properties>
</profile>