tweaks: fix some grammar plus a typo in the comments

src/rcfile.c

@@ -511,7 +511,7 @@ bool is_good_file(char *file)
 	if (access(file, R_OK) != 0)
 		return FALSE;
 
-	/* If the thing exists, it may not be a directory nor a device. */
+	/* If the thing exists, it may be neither a directory nor a device. */
 	if (stat(file, &rcinfo) != -1 && (S_ISDIR(rcinfo.st_mode) ||
 				S_ISCHR(rcinfo.st_mode) || S_ISBLK(rcinfo.st_mode))) {
 		rcfile_error(S_ISDIR(rcinfo.st_mode) ? _("\"%s\" is a directory") :

src/text.c

@@ -700,7 +700,7 @@ void do_undo(void)
 	switch (u->type) {
 	case ADD:
 		/* TRANSLATORS: The next thirteen strings describe actions
-		 * that are undone or redone.  It are all nouns, not verbs. */
+		 * that are undone or redone.  They are all nouns, not verbs. */
 		undidmsg = _("text add");
 		if (u->xflags == WAS_FINAL_LINE && !ISSET(NO_NEWLINES))
 			remove_magicline();

src/winio.c

@@ -984,7 +984,7 @@ int convert_sequence(const int *seq, size_t length, int *consumed)
 				}
 				break;
 #ifndef NANO_TINY
-			case '9': /* To accomodate iTerm2 in "xterm mode". */
+			case '9': /* To accommodate iTerm2 in "xterm mode". */
 			case '3':
 				switch (seq[4]) {
 					case 'A': /* Esc [ 1 ; 3 A == Alt-Up on xterm. */