In mpfr.texi, added a "@." to avoid a warning from mpfrlint.

Note: This is not needed at the end of a paragraph like here, but
this is a general warning, just in case text is added or moved.

doc/mpfr.texi

@@ -253,7 +253,7 @@ will not reflect on our reputation.
 
 The precise conditions of the license for the GNU MPFR library are found in the
 Lesser General Public License that accompanies the source code.
-See the file COPYING.LESSER.
+See the file COPYING.LESSER.@.
 
 @node Introduction to MPFR, Installing MPFR, Copying, Top
 @comment  node-name,  next,  previous,  up