Fix typo in functional dependencies doc

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2772

docs/users_guide/glasgow_exts.rst

@@ -4937,7 +4937,8 @@ Functional dependencies
 
     Allow use of functional dependencies in class declarations.
 
-Functional dependencies are implemented as described by [Jones2000]_.Mark Jones in
+Functional dependencies are implemented as described by Mark Jones in
+[Jones2000]_.
 
 Functional dependencies are introduced by a vertical bar in the syntax
 of a class declaration; e.g. ::