Fix spelling mistakes

library/Icinga/Chart/PieChart.php

@@ -16,7 +16,7 @@ use Icinga\Chart\Render\LayoutBox;
 /**
  * Graphing component for rendering Pie Charts.
  *
- * See the graphs.md documentation for futher information about how to use this component
+ * See the graphs.md documentation for further information about how to use this component
  */
 class PieChart extends Chart
 {

library/Icinga/Chart/Render/RenderContext.php

@@ -132,7 +132,7 @@ class RenderContext
      * @param   int $x  The relative x coordinate
      * @param   int $y  The relative y coordinate
      *
-     * @return  array   An x,y tupel containing absolute coordinates
+     * @return  array   An x,y tuple containing absolute coordinates
      * @see     RenderContext::toRelative
      */
     public function toAbsolute($x, $y)