Fix --output parameter in mongoexport to --out

mongoexport doesn't have any --output parameter.

Author: Siddharth Singh

source/reference/mongoexport.txt

@@ -178,7 +178,7 @@ format into a file located at ``/opt/backups/contacts.csv``.
 
 .. code-block:: sh
 
-   mongoexport --db users --collection contacts --csv --output /opt/backups/contacts.csv
+   mongoexport --db users --collection contacts --csv --out /opt/backups/contacts.csv
 
 The next example creates an export of the collection ``contacts``
 from the MongoDB instance running on the localhost port number ``27017``,
@@ -187,7 +187,7 @@ with journaling explicitly enabled. This writes the export to the
 
 .. code-block:: sh
 
-   mongoexport --db sales --collection contacts --output contacts.json --journal
+   mongoexport --db sales --collection contacts --out contacts.json --journal
 
 The following example exports the collection ``contacts`` from the
 ``sales`` database located in the MongoDB data files located at
@@ -212,4 +212,4 @@ located on the host ``mongodb1.example.net`` running on port
 
 .. code-block:: sh
 
-   mongoexport --host mongodb1.example.net --port 37017 --username user --password pass --collection contacts --db marketing --output mdb1-examplenet.json
+   mongoexport --host mongodb1.example.net --port 37017 --username user --password pass --collection contacts --db marketing --out mdb1-examplenet.json