VERCEL_GITHUB_COMMIT_SHA → VERCEL_GIT_COMMIT_SHA (#3337)

* Update gatsby-node.js

* remove additional vercel fallbacks

Author: Cameron McEfee

packages/gatsby/gatsby-node.js

@@ -6,9 +6,7 @@ const sentryRelease = JSON.stringify(
     // Netlify - https://docs.netlify.com/configure-builds/environment-variables/#build-metadata
     process.env.COMMIT_REF ||
     // Vercel - https://vercel.com/docs/v2/build-step#system-environment-variables
-    process.env.VERCEL_GITHUB_COMMIT_SHA ||
-    process.env.VERCEL_GITLAB_COMMIT_SHA ||
-    process.env.VERCEL_BITBUCKET_COMMIT_SHA ||
+    process.env.VERCEL_GIT_COMMIT_SHA ||
     // Zeit (now known as Vercel)
     process.env.ZEIT_GITHUB_COMMIT_SHA ||
     process.env.ZEIT_GITLAB_COMMIT_SHA ||