[conv.qual] Fix typo "desecender"

Author: jwilk

source/conversions.tex

@@ -253,7 +253,7 @@
 if the following conditions are satisfied,
 % NB: forbid line break between 'where' and 'cv'
 % to stop superscript j from running into
-% desecender of p on the previous line.
+% descender of p on the previous line.
 where~$cv_i^j$ denotes the cv-qualifiers in the cv-qualification signature of $T_j$%
 \footnote{These rules ensure that const-safety is preserved by the conversion.}: