assoc-in does not add expected newlines

[teodorlu]

Following up on babashka/neil#169.

I get the behavior I expect when the assoc-in path has only one element:

(let [deps-str "
{:deps
 {hiccup {:mvn/version \"1.0.4\"}}}
"]
  (= "
{:deps
 {hiccup {:mvn/version \"1.0.4\"}}
 :aliases {}}
"
     (-> deps-str
         r/parse-string
         (r/assoc-in [:aliases] {})
         str)))
;; => true

I do not get the behavior I expect when the assoc-in path has two elements.

Expected:

(let [deps-str "
{:deps
 {hiccup {:mvn/version \"1.0.4\"}}}
"]
  (= "
{:deps
 {hiccup {:mvn/version \"1.0.4\"}}
 :aliases {:neil {}}}
"
     (-> deps-str
         r/parse-string
         (r/assoc-in [:aliases :neil] {})
         str)))

Actual:

(let [deps-str "
{:deps
 {hiccup {:mvn/version \"1.0.4\"}}}
"]
  (= "
{:deps
 {hiccup {:mvn/version \"1.0.4\"}} :aliases {:neil {}}}
"
     (-> deps-str
         r/parse-string
         (r/assoc-in [:aliases :neil] {})
         str)))
;; => true

In other words, :aliases {:neil {}} shows up on the same line as hiccup, when I'd like to see it printed on its own line.