use xdg cache dir instead of data

Author: lightclient

src/engine/authentication.md

@@ -44,11 +44,11 @@ If no existing JWT is located, the client **MUST** generate such a token, valid
 ### Default JWT secret locations
 
 For Linux:
-* `$XDG_DATA_DIR/ethereum/engine/jwt.hex`
-* `$HOME/.local/share/ethereum/engine/jwt.hex`
+* `$XDG_CACHE_DIR/ethereum/engine/jwt.hex`
+* `$HOME/.cache/ethereum/engine/jwt.hex`
 
 For Mac:
-* `$HOME/Library/Application Support/Ethereum/Engine/jwt.hex`
+* `$HOME/Library/Caches/Ethereum/Engine/jwt.hex`
 
 For Windows:
 * `%LocalAppData%/Ethereum/Engine/jwt.hex`