[iterator.concept.winc] Fix typo (#6800)

Author: Andreas-Krug

source/iterators.tex

@@ -1551,7 +1551,7 @@
 
 \pnum
 \recommended
-The implementaton of an algorithm on a weakly incrementable type
+The implementation of an algorithm on a weakly incrementable type
 should never attempt to pass through the same incrementable value twice;
 such an algorithm should be a single-pass algorithm.
 \begin{note}