[gdb/cli] Fix help text of maint info target-sections

I noticed a typo:
...
(gdb) help maint info target-sections
List GDB's internal section table.

Print the current targets section list.  This is a sub-set of all
sections, from all objects currently loaded.  Usually the ALLOC
sectoins.
...

Fix this by using "sections".

Reviewed-By: Tom Tromey <tom@tromey.com>

gdb/maint.c

@@ -1259,7 +1259,7 @@ List GDB's internal section table.\n\
 \n\
 Print the current targets section list.  This is a sub-set of all\n\
 sections, from all objects currently loaded.  Usually the ALLOC\n\
-sectoins."),
+sections."),
 	   &maintenanceinfolist);
 
   add_basic_prefix_cmd ("print", class_maintenance,