Fix broken link to MurmurHash source (#2476)

Author: matchai

packages/hash/README.md

@@ -8,4 +8,4 @@ import hash from '@emotion/hash'
 hash('some-string') // 12fj1d
 ```
 
-The source of this is from https://github.com/garycourt/murmurhash-js/blob/main/murmurhash2_gc.js.
+The source of this is from https://github.com/garycourt/murmurhash-js/blob/master/murmurhash2_gc.js.