[alg.equal] Add missing period

Author: jensmaurer

source/algorithms.tex

@@ -3979,7 +3979,7 @@
 \returns
 If \tcode{last1 - first1 != last2 - first2}, return \tcode{false}.
 Otherwise return \tcode{true}
-if $E$ holds for every iterator \tcode{i} in the range \range{first1}{last1}
+if $E$ holds for every iterator \tcode{i} in the range \range{first1}{last1}.
 Otherwise, returns \tcode{false}.
 
 \pnum