Minor grammar fix in Summary

Author: Brian Thomas

acfits.tex

@@ -1594,7 +1594,7 @@ \section{Summary -- Significant problems exist in the FITS standard}
 
 \item FITS lacks a standard mechanism for associating data models with one another.
 
-\item FITS lacks support for missing values for floating point data.
+\item FITS lacks support for missing values in floating point data.
 
 \end{itemize}