Fix a typo

Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>

doc/man/zathurarc.5.rst

@@ -741,7 +741,7 @@ Defines the column in which the first page will be displayed.
 This setting is stored separately for every value of pages-per-row according to
 the following pattern <1 page per row>:[<2 pages per row>[: ...]]. The last
 value in the list will be used for all other number of pages per row if not set
-explicitely.
+explicitly.
 
 Per default, the first column is set to 2 for double-page layout.