Merge pull request #1154 from samsosa/master

Simple copy & paste error fixed, GetMaxX must return width not height.

src/ImageSharp/Common/Helpers/ImageMaths.cs

@@ -359,7 +359,7 @@ namespace SixLabors.ImageSharp
                     }
                 }
 
-                return height;
+                return width;
             }
 
             topLeft.Y = GetMinY(bitmap);