Typo fix in install-mongo-on-ubuntu

Author: dandv

source/tutorial/install-mongodb-on-ubuntu.txt

@@ -83,7 +83,7 @@ to import the `10gen public GPG Key <http://docs.mongodb.org/10gen-gpg-key.asc>`
 
    sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10
 
-Create a the ``/etc/apt/sources.list.d/10gen.list`` file and include
+Create a ``/etc/apt/sources.list.d/10gen.list`` file and include
 the most appropriate version of the following lines for the 10gen
 repository.