Added snippetReplacements to allowed labs flags

refs https://github.com/TryGhost/Team/issues/973

- alpha flag for Admin feature that allows for replacing a snippet's content without having to delete and recreate it manually

core/shared/labs.js

@@ -30,7 +30,8 @@ const ALPHA_FEATURES = [
     'oauthLogin',
     'membersFiltering',
     'emailOnlyPosts',
-    'dashboardTwo'
+    'dashboardTwo',
+    'snippetReplacements'
 ];
 
 module.exports.WRITABLE_KEYS_ALLOWLIST = [...BETA_FEATURES, ...ALPHA_FEATURES];