Update Font.php

When setting vertical position to "top" ImageMagic requires the "Vertical offset in pixels to the baseline of text" according to 
http://php.net/manual/en/imagick.annotateimage.php.
Therefore we actually need the yOffset + the characterHeight

src/Intervention/Image/Imagick/Font.php

@@ -67,7 +67,7 @@ class Font extends \Intervention\Image\AbstractFont
                 break;
 
                 case 'top':
-                $posy = $posy + $dimensions['textHeight'] * 0.65;
+                $posy = $posy + $dimensions['characterHeight'];
                 break;
             }
         }