patch 8.2.3914: various spelling mistakes in comments

Problem:    Various spelling mistakes in comments.
Solution:   Fix the mistakes. (Dominique Pellé, closes #9416)

src/os_mac_conv.c

@@ -258,7 +258,7 @@ enc2macroman(
 		kCFStringEncodingMacRoman,
 		0, // no lossy conversion
 		0, // not external representation (since vim
-		   // handles this internally
+		   // handles this internally)
 		to, maxtolen, &l))
     {
 	CFRelease(cfstr);