fix checkstyle warnings

Author: James Lee

server/src/main/java/com/example/Greeter.java

@@ -12,8 +12,11 @@ public Greeter() {
 
   }
 
-  //TODO: Add javadoc comment
-  public String greet(String someone) {
+  /**
+   * @param someone the name of a person
+   * @return greeting string
+   */
+  public final String greet(final String someone) {
     return String.format("Hello, %s!", someone);
   }
 }

server/src/main/java/com/example/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * This is a package name.
+ */
+package com.example;