change tutorial to use enum name instead of value (#8783)

* change tutorial to use enum name instead of value

* use enum name instead of value

doc/tutorials/core/mat_operations.markdown

@@ -14,7 +14,7 @@ Load an image from a file:
 If you read a jpg file, a 3 channel image is created by default. If you need a grayscale image, use:
 
 @code{.cpp}
-    Mat img = imread(filename, 0);
+    Mat img = imread(filename, IMREAD_GRAYSCALE);
 @endcode
 
 @note format of the file is determined by its content (first few bytes) Save an image to a file:

doc/tutorials/introduction/load_save_image/load_save_image.markdown

@@ -28,7 +28,7 @@ int main( int argc, char** argv )
  char* imageName = argv[1];
 
  Mat image;
- image = imread( imageName, 1 );
+ image = imread( imageName, IMREAD_COLOR );
 
  if( argc != 2 || !image.data )
  {