vim-patch:8.1.0528: various typos in comments

Problem:    Various typos in comments.
Solution:   Fix the typos.
c4568ab37e

src/nvim/spell.c

@@ -2294,7 +2294,7 @@ static void use_midword(slang_T *lp, win_T *wp)
 }
 
 // Find the region "region[2]" in "rp" (points to "sl_regions").
-// Each region is simply stored as the two characters of it's name.
+// Each region is simply stored as the two characters of its name.
 // Returns the index if found (first is 0), REGION_ALL if not found.
 static int find_region(char_u *rp, char_u *region)
 {