Pre: Prefer [(pred ...)] to [[pred ...]] syntax.

This is a style choice.  We supported both, perhaps for Datomic
compliance, but it's not the standard we use in our code base.  In
addition, it doesn't read like lisp (which is what EDN is copying),
since [] is not function application in most lisps.

It's also a convenience: I don't want to parse brackets that have to
agree with `rust-peg`.  It's not hard but it's also not worth doing.

query-algebrizer/src/clauses/not.rs

@@ -338,7 +338,7 @@ mod testing {
             [:find ?x ?age
              :where
              [?x :foo/age ?age]
-             [[< ?age 30]]
+             [(< ?age 30)]
              (not [?x :foo/knows "John"]
                   [?x :foo/knows "Daphne"])]"#;
         let cc = alg(&schema, query);

query-algebrizer/src/clauses/or.rs

@@ -973,7 +973,7 @@ mod testing {
             [:find ?x ?age
              :where
              [?x :foo/age ?age]
-             [[< ?age 30]]
+             [(< ?age 30)]
              (or [?x :foo/knows "John"]
                  [?x :foo/knows "Daphne"])]"#;
         let cc = alg(known, query);