Merge pull request #505 from bjh21/bjh21-test-readatom

Step 6: Test read-string of a single atom at the end of input

Author: kanaka

impls/tests/step6_file.mal

@@ -9,6 +9,9 @@
 (read-string "(1 2 (3 4) nil)")
 ;=>(1 2 (3 4) nil)
 
+(= nil (read-string "nil"))
+;=>true
+
 (read-string "(+ 2 3)")
 ;=>(+ 2 3)