Fix typo reported by David Goodger. This closes SF patch #422383.

Doc/ref/ref7.tex

@@ -401,6 +401,6 @@ are class variables; they are shared by all instances.  To define
 instance variables, they must be given a value in the the
 \method{__init__()} method or in another method.  Both class and
 instance variables are accessible through the notation
-```code{self.name}'', and an instance variable hides a class variable
+``\code{self.name}'', and an instance variable hides a class variable
 with the same name when accessed in this way.  Class variables with
 immutable values can be used as defaults for instance variables.