Update doc/ref/grplib.xml

Co-authored-by: Max Horn <max@quendi.de>

doc/ref/grplib.xml

@@ -104,7 +104,7 @@ calculations.
 For groups created as finitely presented groups, including polycyclic groups, the
 generators are labelled, by default, with a letter and a number. Using the
 option <C>generatorNames</C> it is possible to influcence this naming. If
-this option holds a string, the generators are named with this sting and
+this option holds a string, the generators are named with this string and
 numbers, if a list of strings of sufficient length is given, the generator
 names are taken from this list of strings.
 <P/>