[format.string.escaped] Fix typos in "APOSTROPHE"

Author: tkoeppe

source/utilities.tex

@@ -15353,10 +15353,10 @@
 
 \begin{itemize}
 \item
-the result starts and ends with \unicode{0027}{apostrope} (\tcode{'})
+the result starts and ends with \unicode{0027}{apostrophe} (\tcode{'})
 instead of \unicode{0022}{quotation mark} (\tcode{"}), and
 \item
-if \placeholder{C} is \unicode{0027}{apostrope},
+if \placeholder{C} is \unicode{0027}{apostrophe},
 the two characters \tcode{\textbackslash '} are appended to \placeholder{E}, and
 \item
 if \placeholder{C} is \unicode{0022}{quotation mark},