fix typo on encrypt fields page (#379)

Author: Chris Cho

source/fundamentals/encrypt-fields.txt

@@ -66,5 +66,6 @@ The MongoDB manual contains detailed information on the following {+csfle-short+
 - To get started, see the :ref:`{+csfle-short+} Quick Start <csfle-quick-start>`.
 - To learn how to use {+csfle-short+}, see the :ref:`{+csfle-short+} Fundamentals <csfle-fundamentals>`.
 - To learn how to integrate your {+csfle-short+} implementation with a KMS, see the :ref:`{+csfle-short+} Tutorials <csfle-tutorials>`.
-- To learn :{+csfle-short+} concepts, see the :ref:`{+csfle-short+} Reference <csfle-reference>`.
+- To learn {+csfle-short+} concepts, see the :ref:`{+csfle-short+} Reference <csfle-reference>`.
+