fix LaTeX typo in release notes

Author: mflatt

release_notes/release_notes.stex

@@ -116,7 +116,7 @@ Online versions of both books can be found at
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 \section{Functionality Changes}\label{section:functionality}
 
-\subsection{Support for setting the default history file location using the \scheme{CHEZSCHEME_HISTORY environment variable}}
+\subsection{Support for setting the default history file location using the \scheme{CHEZSCHEME_HISTORY} environment variable}
 
 If the environment variable \scheme{CHEZSCHEME_HISTORY} is set during
 startup, and the \scheme{--eehistory} command-line option isn't used,