Remove legacy mongo shell reference from the landing page. (#92)

Author: jdestefano-mongo

source/index.txt

@@ -97,7 +97,7 @@ Learn through examples and best practices
 Zoe works at a university that uses MongoDB to store student records.
 Since her background is in SQL, Zoe reads the
 :manual:`MongoDB Manual </>` to learn how to build queries using the
-``mongo`` shell. 
+MongoDB Shell.
 
 .. cta::