fix (mongodb#227)

Author: mongoKart

source/fundamentals/gridfs.txt

@@ -242,7 +242,7 @@ Download Files
 
 You can download a GridFS file in one of the following ways:
 
-- Use the ``DowloadToStream()`` method to download a file to an output stream.
+- Use the ``DownloadToStream()`` method to download a file to an output stream.
 - Use the ``OpenDownloadStream()`` method to open an input stream.
 
 Download a File to an Output Stream