Set maven java version to 1.8

Author: marci4

pom.xml

@@ -10,6 +10,8 @@
     <description>A barebones WebSocket client and server implementation written 100% in Java</description>
     <url>https://github.com/TooTallNate/Java-WebSocket</url>
     <properties>
+        <maven.compiler.target>1.8</maven.compiler.target>
+        <maven.compiler.source>1.8</maven.compiler.source>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <slf4j.version>2.0.16</slf4j.version>