update outdated headers

xchart-demo/src/main/java/org/knowm/xchart/standalone/AdvancedExample.java

 /**
- * Copyright 2013 Xeiam LLC.
+ * Copyright 2015-2016 Knowm Inc. (http://knowm.org) and contributors.
+ * Copyright 2011-2015 Xeiam LLC (http://xeiam.com) and contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

xchart-demo/src/main/java/org/knowm/xchart/standalone/IntermediateExample.java

 /**
- * Copyright 2013 Xeiam LLC.
+ * Copyright 2015-2016 Knowm Inc. (http://knowm.org) and contributors.
+ * Copyright 2011-2015 Xeiam LLC (http://xeiam.com) and contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

xchart-demo/src/main/java/org/knowm/xchart/standalone/PieChartDemo.java

 /**
- * Copyright 2013 Xeiam LLC.
+ * Copyright 2015-2016 Knowm Inc. (http://knowm.org) and contributors.
+ * Copyright 2011-2015 Xeiam LLC (http://xeiam.com) and contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

xchart-demo/src/main/java/org/knowm/xchart/standalone/SimplestExample.java

 /**
- * Copyright 2013 Xeiam LLC.
+ * Copyright 2015-2016 Knowm Inc. (http://knowm.org) and contributors.
+ * Copyright 2011-2015 Xeiam LLC (http://xeiam.com) and contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.