steps 1 and 9: Test that hash-map keys stay as strings.

Specifically, test that when "1" is used as a hash-map key, it is
represented as a string when printed (step 1) and when returned by
'keys' (step 9).  PHP used to get both of these wrong.

tests/step1_read_print.mal

@@ -155,6 +155,8 @@ false
 ;=>{"a" {"b" {"cde" 3}}}
 {  :a  {:b   {  :cde     3   }  }}
 ;=>{:a {:b {:cde 3}}}
+{"1" 1}
+;=>{"1" 1}
 
 ;; Testing read of comments
  ;; whole line comment (not an exception)

tests/step9_try.mal

@@ -233,6 +233,9 @@
 (keys hm2)
 ;=>("a")
 
+(keys {"1" 1})
+;=>("1")
+
 ;;; TODO: fix. Clojure returns nil but this breaks mal impl
 (vals hm1)
 ;=>()