Refactor: change "folder" to "directory" where needed.

This commit fixes every instance in which the word "folder" is
incorrectly used instead of "directory".

pages/linux/mkisofs.md

@@ -1,12 +1,12 @@
 # mkisofs
 
-> Create ISO files from folders.
+> Create ISO files from directories.
 > Also aliased as `genisoimage`.
 
-- Create an ISO from a folder:
+- Create an ISO from a directory:
 
-`mkisofs -o {{filename.iso}} {{path/to/source_folder}}`
+`mkisofs -o {{filename.iso}} {{path/to/source_directory}}`
 
 - Set the disc label when creating an ISO:
 
-`mkisofs -o {{filename.iso}} -V {{"label_name"}} {{path/to/source_folder}}`
+`mkisofs -o {{filename.iso}} -V {{"label_name"}} {{path/to/source_directory}}`