Make shellcheck (slightly) more happy

… though `dash` still doesn’t work. ;<

fedi2html

@@ -114,7 +114,7 @@ render_responses() (
 "
 
 	for response in $responses; do
-		render_post "$response" "$responses_data" "$(expr "$level" + 1)"
+		render_post "$response" "$responses_data" "$((level + 1))"
 	done
 )
 
@@ -267,7 +267,7 @@ url_post_id() (
 url_server() (
 	url="$1"
 	protocol="$(echo "$url" | grep --only-matching '[[:alnum:]]*://')"
-	printf "$protocol"
+	printf '%s' "$protocol"
 	echo "$url" \
 		| sed 's%^'"$protocol"'%%' \
 		| sed 's%/.*%%'
@@ -432,6 +432,8 @@ while getopts 'hcIRt:bm:B' arg; do
 		B)
 			EXCLUDE_REPLIES="true"
 			;;
+		*)
+			;;
 	esac
 done