Set main as the default branch (#527)

* set main as the default branch

* revert change to tool-cache default branch

* use versions where applicable

src/context.ts

@@ -1,4 +1,4 @@
-// Originally pulled from https://github.com/JasonEtco/actions-toolkit/blob/master/src/context.ts
+// Originally pulled from https://github.com/JasonEtco/actions-toolkit/blob/main/src/context.ts
 import {WebhookPayload} from './interfaces'
 import {readFileSync, existsSync} from 'fs'
 import {EOL} from 'os'