parser: Fix parsing of arrow “px -> …”
The parser failed to read the profile name after the the arrow. Rules with
-> foo-bar; failed with “Found unexpected character: '-'”. Rules with
-> @{tgt}; compiled fine, but failed at runtime with “profile transition
not found”.
The patch was written by sbeattie and published on https://paste.ubuntu.com/p/tzxxmVwGJ8/