Update grammar file to match Cromwell supported WDL version

grammar.hgr

@@ -130,7 +130,11 @@ grammar {
       r'>=' -> :gteq
       r'>' -> :gt
       r'!' -> :not
-
+      enum {
+        python: r'\?'
+        java: "\\?"
+        javascript: "\\?"
+      } -> :qmark
       # Literals
       enum {
         python: r'"([^\\\"\n]|\\[\\"\'nrbtfav\?]|\\[0-7]{1,3}|\\x[0-9a-fA-F]+|\\[uU]([0-9a-fA-F]{4})([0-9a-fA-F]{4})?)*"'