add gumroad icon

src/lib/cards/social/BigSocialCard/index.ts

···
 	siLine,
 	siArchiveofourown,
 	siKickstarter,
+	siGumroad,
 	type SimpleIcon
 } from 'simple-icons';
 
···
 	ao3: /(?:archiveofourown\.org)/i,
 
 	kickstarter: /(?:kickstarter\.com)/i,
+	gumroad: /(?:gumroad\.com)/i,
 
 	germ: /(?:ger\.mx)/i,
 
···
 	ao3: siArchiveofourown,
 
 	kickstarter: siKickstarter,
+	gumroad: siGumroad,
 
 	tangled: {
 		slug: 'tangled',