Fixed repository link in old packages

- these are some of our first packages here and use `master` in their
  repository link
- we've since switched the repo to use `main` but these links were not
  updated
- this commit updates the links

ghost/magic-link/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@tryghost/magic-link",
   "version": "1.0.18",
-  "repository": "https://github.com/TryGhost/Members/tree/master/packages/magic-link",
+  "repository": "https://github.com/TryGhost/Members/tree/main/packages/magic-link",
   "author": "Ghost Foundation",
   "license": "MIT",
   "main": "index.js",

ghost/members-api/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@tryghost/members-api",
   "version": "5.0.1",
-  "repository": "https://github.com/TryGhost/Members/tree/master/packages/members-api",
+  "repository": "https://github.com/TryGhost/Members/tree/main/packages/members-api",
   "author": "Ghost Foundation",
   "license": "MIT",
   "main": "index.js",

ghost/members-csv/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@tryghost/members-csv",
   "version": "1.2.4",
-  "repository": "https://github.com/TryGhost/Members/tree/master/packages/members-csv",
+  "repository": "https://github.com/TryGhost/Members/tree/main/packages/members-csv",
   "author": "Ghost Foundation",
   "license": "MIT",
   "main": "index.js",

ghost/members-ssr/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@tryghost/members-ssr",
   "version": "1.0.20",
-  "repository": "https://github.com/TryGhost/Members/tree/master/packages/members-ssr",
+  "repository": "https://github.com/TryGhost/Members/tree/main/packages/members-ssr",
   "author": "Ghost Foundation",
   "license": "MIT",
   "main": "index.js",