allow full expr in hint_value

Author: mlin

WDL/_grammar.py

@@ -95,7 +95,7 @@
 hints_section: hints_object
 hints_object: "hints" "{" [hint_kv (","? hint_kv)*] ","? "}"
 hint_kv: CNAME ":" hint_value
-?hint_value: literal | string_literal | hints_object | io_hint
+?hint_value: expr | hints_object | io_hint
 io_hint: ("input" | "output") "{" [io_hint_kv ("," io_hint_kv)*] ","? "}"
 io_hint_kv: CNAME ("." CNAME)* ":" hint_value